Wound treatment apparatus and method

ABSTRACT

An apparatus for cleansing wounds in which irrigant fluid from a reservoir connected to a conformable wound dressing and wound exudate from the dressing are moved by a device (which may be a single pump or two pumps) for moving fluid through a flow path which passes through the dressing and a means for providing simultaneous aspiration and irrigation of the wound. The apparatus also comprises means to apply high frequency vibrational energy, e.g. ultrasound, to the wound bed. The former removes materials deleterious to wound healing, while distributing materials that are beneficial in promoting wound healing over the wound bed. The latter promotes healing. The dressing and a method of treatment using the apparatus.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/919,354, filed Nov. 19, 2008, entitled “WOUND TREATING APPARATUS ANDMETHOD,” and issued as U.S. Pat. No. 9,044,579, which is a U.S. NationalPhase of PCT International Application No. PCT/GB/2006/001552, filedApr. 27, 2006, designating the United States and published in English onNov. 2, 2006, as International Publication No. WO 2006/114638 A2, whichapplication claims priority to Great Britain Patent Application No.0508531.1, filed Apr. 27, 2005. The disclosures of the priorapplications are incorporated by reference herein in their entiretiesand should be considered a part of this application.

BACKGROUND

1. Technical Field

The present invention relates to apparatus and a medical wound dressingfor aspirating, irrigating and/or cleansing wounds, and a method oftreating wounds using such apparatus for aspirating, irrigating and/orcleansing wounds.

It relates in particular to such an apparatus, wound dressing and methodthat can be easily applied to a wide variety of, but in particularchronic, wounds, to cleanse them of materials that are deleterious towound healing, whilst distributing materials that are beneficial in sometherapeutic aspect, in particular to wound healing.

2. Description of the Related Art

Aspirating and/or irrigating apparatus are known, and tend to be used toremove wound exudate during wound therapy. In known forms of such woundtherapy, aspiration and irrigation of the wound generally take placesequentially.

Each part of the therapy cycle is beneficial in promoting wound healing:

Aspiration applies a negative pressure to the wound, which is beneficialin itself in promoting wound healing by removing materials deleteriousto wound healing with the wound exudate, reducing bacterial load,combating peri-wound oedema, increasing local blood flow to the woundand encouraging the formation of wound bed granulation tissue.

Irrigation cleanses wounds of materials that are deleterious to woundhealing by diluting and moving wound exudate (which is typicallyrelatively little fluid and may be of relatively high viscosity andparticulate-filled.

Additionally, relatively little of beneficial materials involved inpromoting wound healing (such as cytokines, enzymes, growth factors,cell matrix components, biological signalling molecules and otherphysiologically active components of the exudate) are present in awound, and are not well distributed in the wound, i.e. they are notnecessarily present in parts of the wound bed where they can bepotentially of most benefit. These may be distributed by irrigation ofthe wound and thus aid in promoting wound healing.

The irrigant may additionally contain materials that are potentially oractually beneficial in respect of wound healing, such as nutrients forwound cells to aid proliferation, and gases, such as oxygen. These maybe distributed by irrigation of the wound and thus aid in promotingwound healing.

If aspiration and irrigation therapy is applied sequentially to a wound,the two therapies, each of which is beneficial in promoting woundhealing, can only be applied intermittently.

Thus, the wound will lose the abovementioned known beneficial effects ofaspiration therapy on wound healing, at least in part, while thataspiration is suspended during irrigation.

Additionally, for a given aspirate flow, whilst materials that arepotentially or actually deleterious in respect of wound healing areremoved from wound exudate, the removal in a given time period ofapplication of the total irrigate and/or aspirate therapy will normallybe less effective and/or slower than with continuous application ofaspiration.

Even less to be desired, is that while aspiration is not applied to thewound, wound exudate and materials deleterious to wound healing (such asbacteria and debris, and iron II and iron Ill and for chronic woundsproteases, such as serine proteases) will pool on the wound bed andhinder wound healing, especially in a highly exuding wound. The influxof local oedema will also add to the chronicity of the wound. This isespecially the case in chronic wounds.

Depending on the relative volumes of irrigant and wound exudate, themixed exudate-irrigant fluid and may be of relatively high viscosityand/or particulate-filled. Once it is present and has pooled, it may bemore difficult to shift by the application of aspiration in aconventional sequential aspirate irrigate—dwell cycle than withcontinuous simultaneous aspiration and irrigation of the wound, owing tothe viscosity and blockage in the system.

The wound will also lose the abovementioned beneficial effects ofirrigation therapy on wound healing, at least in part, while thatirrigation is suspended during aspiration.

These benefits in promoting wound healing include the movement ofmaterials that are beneficial in promoting wound healing, such as thosementioned above.

Additionally, for a given irrigant flow, the Cleansing of the wound andthe distribution by irrigation of the wound of such beneficial materialsin a given time period of application of the total irrigate and/oraspirate therapy when such therapy is in a conventional sequentialaspirate—irrigate—dwell cycle will normally be less effective and/orslower than with continuous application of aspiration.

Such known forms of aspiration and/or irrigation therapy systems alsooften create a wound environment that may result in the loss of optimumperformance of the body's own tissue healing processes, and slow healingand/or in weak new tissue growth that does not have a strongthree-dimensional structure adhering well to and growing from the woundbed. This is a significant disadvantage, in particular in chronicwounds.

SUMMARY

The relevant devices tend not to be portable.

It thus would be desirable to provide a system of aspiration andirrigation therapy for a wound, which can remove wound exudate andmaterials deleterious to wound healing from contact with the wound bed,whilst simultaneously cleansing it and distributing materials that arebeneficial in promoting wound healing across it.

It is further desirable to provide a system which: obviates at leastsome of the abovementioned disadvantages of known aspiration and/orirrigation systems, and is portable.

Vascular supply to, and aspiration in, tissue underlying and surroundingthe wound is often compromised.

It is further desirable to provide a system of therapy that alsopromotes vascular supply to tissue underlying and surrounding a wound,promoting wound healing.

Additionally, known forms of wound dressing and aspiration and/orirrigation therapy systems often create a wound environment under thebacking layer that may result in the loss of optimum performance of thebody's own tissue healing processes, and slow healing and/or in weak newtissue growth that does not have a strong three-dimensional structureadhering well to and growing from the wound bed. This is a significantdisadvantage, in particular in chronic wounds.

High frequency vibrational, in particular ultrasonic, energy on and/orin a wound bed surface has been found to result in improved cellproliferation and accelerated growth of tissue whilst resulting in animproved breaking strength of tissue growth that has a strongthree-dimensional structure adhering well to and growing from the woundbed, and reduction of wound recurrence.

High frequency vibrational, in particular ultrasonic, energy across thewound bed may also advantageously act against wound bacteria, bybreaking up biofilm growth before it develops a strong three-dimensionalstructure adhering well to and growing from the wound bed, releasingthem to be attacked by the body in the wound, and/or breaking up thebacterial cell wall at higher intensities.

It may aid in the debridement of slough, eschar and necrotic tissuegrowth from the wound.

It is an object of the present invention to provide a system of therapywhich i) remove materials deleterious to wound healing from woundexudate, and ii) which creates high frequency vibrational energy, inparticular ultrasonic, energy on and/or in a wound bed surface.

The application of high frequency vibrational energy is equallyapplicable to both sequential systems (i.e., empty/fill cycles) orsimultaneous irrigation/aspiration systems. Although it is generallypreferred to use a simultaneous system, there may be circumstances wherea sequential system is preferred, e.g. due to cost.

According to a first aspect of the present invention there is providedan apparatus for aspirating, irrigating and/or cleansing wounds,comprising a) a fluid flow path, comprising a conformable wounddressing, having a backing layer which is capable of forming arelatively fluid-tight seal or closure over a wound and at least onepipe, which passes through and/or under the wound-facing face to allowirrigation and/or aspiration of the wound, wherein the point at whichthe or each inlet pipe and the or each outlet pipe passes through and/orunder the wound-facing face forming a relatively fluid tight seal orclosure over the wound; b) a fluid reservoir connected by a fluid supplytube to the at least one pipe; c) at least one device for moving fluidthrough the wound dressing; characterized in that it comprises d) meansfor applying high frequency vibrational, in particular ultrasonic,energy to the wound bed.

Generally it is preferred that the apparatus has at least one inlet pipefor connection to a fluid supply tube to allow irrigation and at leastone outlet pipe for connection to a fluid offtake tube to allowaspiration, each of which passes through and/or under the wound-facingface.

Such an embodiment is suitable for both sequential and simultaneoussystems, whereas a single pipe system is only suitable for sequentialfill/empty cycles.

In one embodiment the present invention provides means for providingsimultaneous irrigation and aspiration of the wound, such that fluid maybe supplied to fill the flow path from the fluid reservoir via the fluidsupply tube (optionally via means for supply flow regulation) whilefluid is aspirated by a device through the fluid offtake tube(optionally or as necessary via means for aspirate flow regulation).

Such an embodiment is particularly suitable for simultaneous irrigationand aspiration and thus forms a preferred embodiment by the presentinvention.

Where any pipe is described in connection with the apparatus as beingconnected or for connection to a (mating end of a) tube, e.g. a, fluidsupply tube or fluid offtake tube, the pipe and the tube may form asingle integer in the flow path through which fluid passes.

The means for applying high frequency vibrational, in particularultrasonic, energy to the wound bed via the irrigant fluid and/or woundexudate may be an high frequency vibrational, in particular ultrasonic,sonode and/or a component of the apparatus flow path connected to asonode, the sonic conductivity of which is sufficient for it to functionas an high frequency vibrational, in particular ultrasonic, conductor.

The source of the ultrasound field may be integral with the sonode, orit may be connected to it by means for an high frequency vibrational, inparticular ultrasonic, connection, typically a sonically insulated butconductive waveguide.

The desired or optimum intensities and frequencies of such ultrasoundacross the wound bed for the stimulation of the healing of wounds willsubstantially determine a) the position along the apparatus flow path orthe component of the apparatus flow path where the means for applyinghigh frequency vibrational, in particular ultrasonic, energy to thewound bed and/or conductively heated component of the apparatus flowpath is mounted relative to the dressing; b) the flow rate of irrigantfluid and/or wound exudate; c) the intensity of ultrasound at the pointof supply of energy to apparatus that is necessary given the level ofenergy loss in the system in which the fluid moves and energy isconducted to the wound; and/or d) the nature of the ultrasound source.

Subject to the above, the means to provide high frequency vibrationalenergy may be at any convenient or appropriate position or component ofthe apparatus flow path.

Examples include a means for applying high frequency vibrational, inparticular ultrasonic, energy to the wound bed and/or conductivelyconnected component of the apparatus flow path a) mounted distally ofthe body on, in or inside of the dressing; b) mounted in, on, at or nearone or more of the fluid inlet pipe(s) and outlet pipe(s) that passthrough and/or under the wound-facing face of the backing layer; c)mounted in, on, at or near one or more of the connectors in the tubesthat form the flow path of the apparatus; and/or d) mounted in, on, ator near the reservoir.

Often, the level of energy loss in the system in which the fluid movesand energy is conducted to the wound; and/or the nature of theultrasound source. means that a convenient or appropriate position orcomponent of the apparatus flow path for applying high frequencyvibrational, in particular ultrasonic, energy to the wound bed and/orconductively connected component of the apparatus flow path is on, in orinside of the dressing and/or in, on, at or near one or more of thefluid inlet pipe(s) and outlet pipe(s) that pass through and/or underthe wound-facing face of its backing layer.

In order to effectively deliver high-frequency vibrational, inparticular ultrasonic, energy, as an energy field to the wound bedand/or the fluid thereover, there needs to be a suitably conductivebridge between the wound bed surface and the ultrasound sonode. Water isa good transfer medium of ultrasound, so the presence of a substantiallycontinuous bridge of wound fluid and/or irrigant should provide adequateenergy transfer.

Both longitudinal and shear waves generated by a transducer mechanismand/or shear waves generated by such longitudinally propagating wavesprovide effective healing of wounds.

All these types of waves may propagate directly to the wound. Topicallyapplied longitudinal waves may also be reflected by underlying bonetissue and skin layers and these and shear waves generated by thempropagate towards the wound for the healing thereof

The transducer should be arranged having an operating surface, with thetransducer, disposed substantially adjacent to the wound to emit ultrasound to propagate in the direction of the wound for healing thereof.

As shown in FIG. 14, the transducer 500 may include an axis and afocusing element 502 for focusing the propagation of the ultrasound at apredetermined angle with respect to the axis.

The format of such transducers are described in detail in WO 99/56829,WO 99/48621 and U.S. Pat. No. 5,904,659, all of which are incorporatedherein by way of reference.

High frequency vibrational, in particular ultrasonic, energy, as isapplied in the invention as an ultrasound field to the wound bed and/orthe fluid thereover is characterized by parameters such as intensity,frequency, wave form and whether it is slow-pulsed either regularly orrandomly on the overall ultrasound waveform.

Examples of suitable intensities of ultrasound applied include a spatialpeak temporal average acoustic intensity between 5-100 mW/cm², e.g. 10to 75 mW/cm², such as 30 to 50 mW/cm². When the ultrasound isslow-pulsed, this allows higher peak intensities.

Higher intensity ultrasound is more for hospital use, where relativelyhigh intensities and/or pulsing can only be used safely withprofessional supervision, or for field hospital use.

Examples of suitable frequencies of ultrasound across the wound bed forthe stimulation of the healing of wounds include in general anultrasound carrier frequency between 20 kHz and 10 MHz, such as 60 kHzto 5 MHz, such as 200 kHz to 3 MHz.

It will be understood that where any layers of dressing or apparatus liebetween the source of ultrasound and the wound bed, it may be necessaryto increase the intensity and/or other properties of the ultrasound totake account of attenuation or other factors which affect the deliveryof ultrasound energy to the wound bed.

Examples of suitable waveforms of ultrasound across the wound bed forthe stimulation of the healing of such wounds include those described indetail in WO 99/56829, WO 99/48621 and U.S. Pat. No. 5,904,659, all ofwhich are incorporated herein by way of reference optionally slow-pulsedeither regularly or randomly on the overall ultrasound waveform.

These may be optionally slow-pulsed either regularly or randomly on theoverall vibrational waveform with a relatively low-frequency modulatingsignal.

Examples of suitable pulsing of ultrasound on/across the wound bed forthe stimulation of the healing of wounds include pulsing at lowfrequencies such as 5 Hz to 10 kHz.

Application may be made continuously or intermittently, for example 1-4times daily for a period of 20 minutes per application.

As noted above, the apparatus for irrigating, supplying high frequencyvibrational, in particular ultrasonic, energy to and/or cleansing woundsof the present invention is characterized in that it comprises at leastone sonode for applying a vibrational field to the wound bed and/or thefluid thereover.

The source of the sound field may be connected to the sonode by meansfor an high frequency vibrational, in particular ultrasonic, connection,typically a sonically insulated but conductive waveguide, or it may beintegral with or comprise it

In the former case, the source may be of any conventional type, e.g., inthe case of ultrasound, a piezoelectric transducer; or others describedin detail in WO 99/56829, WO 99/48621 and U.S. Pat. No. 5,904,659, allof which are incorporated herein by way of reference.

Suitable materials for the sonode include materials that do not absorbhigh frequency vibrational (e.g. ultrasonic) energy, such as an Exogen™device (produced by Smith & Nephew). Suitable materials for thewaveguides include ultrasound-conductive materials such as thosedescribed in detail in WO 99/56829, WO 99/48621 and U.S. Pat. No.5,904,659, all of which are incorporated herein by way of reference.Examples of instances where the sonode effectively is or is integralwith the ultrasonic source, include a piezoelectric transducer directlyattached to or integral with a component of the apparatus flow path.

Suitable materials for such a piezoelectric transducing sonode includethose described in detail in WO 99/56829, WO 99/48621 and U.S. Pat. No.5,904,659, all of which are incorporated herein by way of reference.

These include synthetic polymeric materials such as certain halogenatedpolyolefins, such as fluorinated olefin polymers and copolymers, such aspolyvinylidene fluoride and copolymers thereof.

Examples of suitable materials also include thermoplastics, andelastomers and elastomer blends, having for example particulatepiezoelectric dispersed through it, such as the certain halogenatedpolyolefins, such as fluorinated olefin polymers and copolymers, such aspolyvinylidene fluoride and copolymers thereof mentioned above; andcertain minerals, such as quartz.

Examples of suitable such thermoplastics materials and elastomers andelastomer blends include synthetic polymeric materials that do notabsorb aqueous fluids, such as polyolefins, such as polyethylene e.g.high-density polyethylene, -polypropylene, copolymers thereof, forexample with vinyl acetate and polyvinyl alcohol, and mixtures thereof;polysiloxanes; polyesters, such as polycarbonates; polyamides, e.g.nylon 6-6 and 6-10; and hydrophobic polyurethanes.

They may be hydrophilic, and thus also include hydrophilicpolyurethanes. They also include thermoplastic elastomers and elastomerblends, for example copolymers, such as ethyl vinyl acetate, optionallyor as necessary blended with high-impact polystyrene.

They further include elastomeric polyurethane, particularly polyurethaneformed by solution casting.

Where the source is or includes a piezoelectric transducer, it will beelectrically stimulated to change shape repeatedly as appropriate ordesired at ultrasonic frequencies by an ultrasonic frequency electricalsignal generator run at the appropriate frequencies.

The sonode or sonode-transducer may be mounted at any convenient orappropriate position or component of the apparatus flow path. Typically,however, as noted above, it is a) mounted distally of the body on, in orinside of the dressing; and/or b) mounted in, on, at or near one or moreof the fluid inlet pipe(s) and outlet pipe(s) that pass through and/orunder the wound-facing face of the backing layer.

It will be so positioned as to apply an ultrasound field to the fluidacross the wound bed and/or to be in contact with the wound bed and/orthe surrounding surfaces of the body. It may be more convenient if thesonode or sonode-transducer is outside the dressing, since otherwise itrequires that a waveguide or electric leads will pass through and/orunder the wound-facing face of the backing layer, and the point at whichit passes or they through and/or under the wound-facing face must form arelatively fluid-tight seal or closure over the wound.

Where the sonode or sonode-transducer is mounted on the dressing, e.g.the backing layer, the wound dressing may then effectively be capable ofbeing electrically stimulated to change shape repeatedly as appropriateor desired at high frequency vibrational, in particular ultrasonic,frequencies.

In all relevant embodiments of the present apparatus where the sonode orsonode-transducer is mounted distally of the body on, in or inside ofthe dressing, it will often be at or near the center of the dressingbacking layer. It may be attached to or integral with it.

Where the sonode-transducer is mounted distally of the body on, in orinside of the dressing, it may be in the form of a relatively laminarinteger, for example a discoidal pellet, foil, film, sheet or membrane.

It may be mounted to be clear of or surround one or more of the fluidinlet pipe(s) and outlet pipe(s) that pass through and/or under thewound-facing face of the backing layer.

The sonode or sonode-transducer may be attached, as appropriate byheat-sealing or by adhesive, or it may be a push, slide, snap ortwist-lock fit.

For example, in the former case, a sonode-transducer such as a film,sheet or membrane of or comprising a piezoelectric transducingpolyolefin, such as polyvinylidene fluoride and copolymers thereof, maybe attached, e.g. by an adhesive, in particular a curable adhesive,coextrusion or heat lamination to the dressing.

It may be mounted distally on the backing layer to be clear of orsurround one or more of the fluid inlet pipe(s) and outlet pipe(s) thatpass through and/or under the wound-facing face of the backing layer.

Alternatively, it may be mounted proximally on the backing layer to beclear of, surround or pass across one or more of the fluid inlet pipe(s)and outlet pipe(s) that pass through and/or under the wound-facing faceof the backing layer.

In the last case, it will have to be mounted on relatively stiff butstill conformable, proximally projecting struts, supports, braces orstays, or on a similar proximally projecting boss to permit ingress oregress of fluid as appropriate.

Where the sonode or sonode-transducer is attached as a push, slide, snapor twist-lock fit, it may for example be mounted distally or proximallyon the backing layer clear of the fluid inlet pipe(s) and outlet pipe(s)that pass through and/or under the wound-facing face of the backinglayer, as a push fit in a (respectively) distally or proximallyprojecting recessed boss.

For example, a sonode such as an Exogen™ device may be a push fit in adistally projecting recessed boss on the distal backing layer surface.

The sonode or is then connected ultrasonically to the dressing backingsheet by a layer of ultrasound coupling material, e.g. a coupling gel,which is needed to transmit the energy to the irrigant and/or exudateunder the wound-facing face of the wound dressing.

A sonode-transducer, for example a disc, film, sheet or membrane, of orcomprising a piezoelectric, such as polyvinylidene fluoride andcopolymers thereof mentioned above, may be mounted at any convenient orappropriate position, in or inside of the dressing, as a push fit in aproximally projecting recessed boss.

Such a sonode/transducer does not need to be connected ultrasonically tothe dressing backing sheet by a layer of ultrasound coupling material,e.g. the adhesive or by a coupling gel, which is needed to transmit theenergy to the irrigant and/or exudate under the wound-facing face of thewound dressing.

However, it requires that electric leads pass through and/or under thewound-facing face of the backing layer, but the point at which they passthrough the wound-facing face is not in contact with fluid, so that theclosure over the wound is not prejudiced.

As noted above, the sonode or sonode-transducer may be mounted in, on,at or near one or more of the fluid inlet pipe(s) and outlet pipe(s)that pass through and/or under the wound-facing face of the backinglayer,

In such case, the nature of the sonode or sonode-transducer, and themanner and position in which it may be mounted are similar to the thosein the case of mounting in or on the dressing mutatis mutandis.

Mounting in, on, at or near one or more of the fluid inlet pipe(s) andoutlet pipe(s) may however be less preferred than mounting on thebacking layer at any convenient or appropriate position, since, becauseof the orientation of the pipes, it may be less easy to direct thehigh-frequency vibrational or ultrasonic energy sufficiently to achieveadequate therapeutic intensities across the wound bed for thestimulation of the healing of wounds.

Suitable dressings are depicted and described in more detailhereinafter.

Where the present invention involves simultaneous irrigation/aspirationit provides several further advantages.

One is that application of an irrigant to a wound under simultaneousaspiration creates a wound environment that is exposed to the continuousbeneficial effects of both aspects of the therapy for wound healing, asopposed to the sequential intermittent application of irrigant flow andaspiration in known aspirating and/or irrigating apparatus. The latterresult in less than optimum performance of the body's own tissue healingprocesses, and slower healing and/or weaker tissue growth that does nothave a strong three-dimensional structure adhering well to and growingfrom the wound bed. This is a significant disadvantage, in particular inchronic wounds.

Such a system is particular suited for removing materials deleterious towound healing with the wound exudate, reducing bacterial load, combatingperi-wound oedema and encouraging the formation of wound bed granulationtissue.

Preferred embodiments of the apparatus of the present invention foraspirating, irrigating and/or cleansing chronic wounds apply a mildernegative pressure than in conventional negative pressure therapy (whichis too aggressive for the fragile tissues of many such wounds). Thisleads to increased patient comfort, and lessens the risk of inflammationof the wound.

The removal of wound exudate in a given time period of application ofthe simultaneous irrigate and/or aspirate therapy will normally be moreeffective and/or faster than with a conventional sequential intermittentaspiration and/or irrigation therapy.

Even more desirably, since simultaneous aspiration and irrigation isapplied to the wound, wound exudate and materials deleterious to woundhealing (such as bacteria and debris, and iron II and iron Ill and forchronic wounds proteases) will not pool on the wound bed and hinderwound healing, especially in a highly exuding wound. This is especiallyimportant in chronic wounds.

The resulting mixed exudate-irrigant fluid will usually be of relativelylower viscosity.

Because simultaneous aspiration and irrigation of the wound providescontinuous removal at a constant relatively high speed, the fluid doesnot have to be accelerated cyclically from rest, and will be easier toshift than with known forms of aspiration and/or irrigation therapysystems with a conventional sequential aspirate—irrigate—dwell cycle.This will thus exert a greater net effect on the removal of adherentbacteria and debris.

This is especially the case in those embodiments of the apparatus of thepresent invention for aspirating, irrigating and/or cleansing woundswhere there is an inlet manifold (as described in further detailhereinafter) that covers and contacts a significant area, preferablymost, of the wound bed with openings that deliver the fluid directly tothe wound bed over an extended area.

It will be seen that the balance of fluid between fluid aspirated fromthe wound and irrigant supplied to the wound from the irrigant reservoirmay provide a predetermined steady state concentration equilibrium ofmaterials beneficial in promoting wound healing over the wound bed.Simultaneous aspiration of wound fluid and irrigation at a controlledflow rate aids in the attainment and maintenance of this equilibrium.

The apparatus for irrigating and/or aspirating wounds of the presentinvention may be used cyclically and/or with reversal of flow.

Preferably the present apparatus for aspirating, irrigating and/orcleansing wounds is a conventionally automated, programmable systemwhich can cleanse the wound with minimal supervision.

The means for providing simultaneous aspiration and irrigation of thewound often comprises a (first) device for moving fluid through thewound applied to fluid downstream of and away from the wound dressing incombination with at least one of a second device for moving fluidthrough the wound applied to the irrigant in the fluid supply tubeupstream of and towards the wound dressing; means for aspirate flowregulation, connected to a fluid offtake tube, and means for supply flowregulation, connected to a fluid supply tube.

The (first) device will apply negative pressure (i.e. below-atmosphericpressure or vacuum) to the wound bed. It may be applied to the aspiratein the fluid offtake tube downstream of and away from the wounddressing.

Alternatively or additionally, where appropriate, the aspirate in thefluid offtake tube downstream of the wound dressing may be aspiratedinto a collection vessel, and the first device may act on fluid such asair from the collection vessel. This prevents contact of the device withthe aspirate.

The (first) device may be a fixed-throughput device, such as afixed-speed pump, which will usually require a discrete means foraspirate flow regulation, connected to a fluid offtake tube, and/ormeans for supply flow regulation, connected to a fluid supply tube, ineach case, e.g. a regulator, such as a rotary valve.

Alternatively, where appropriate the (first) device for moving fluidthrough the wound may be a variable-throughput device, such as avariable-speed pump, downstream of the wound dressing, thus effectivelyforming a combination of a (first) device for moving fluid through thewound with means for aspirate flow regulation and/or means for supplyflow regulation in a single integer.

The (first) device for moving fluid through the wound will often be apump of any of the types set out below, or a piped supply of vacuum,applied to fluid downstream of and away from the wound dressing. In thecase of any pump it may be a fixed-speed pump, with (as above) adiscrete means for aspirate flow regulation, connected to a fluidofftake tube, and/or means for supply flow regulation, connected to afluid supply tube, in each case, e.g. a regulator, such as a rotaryvalve. Alternatively, where appropriate the pump may be avariable-throughput or variable-speed pump.

The following types of pump may be used as the (first) device:

-   -   Reciprocating Pumps, such as Piston Pumps—where pistons pump        fluids through check valves, in particular for positive and/or        negative pressure on the wound bed; and    -   Diaphragm Pumps—where pulsations of one or two flexible        diaphragms displace liquid with check valves        and    -   Rotary Pumps, such as:        -   Progressing Cavity Pumps with a cooperating screw rotor and            stator, in particular for higher-viscosity and particulate            filled exudate; and        -   Vacuum Pumps with pressure regulators.

The (first) device may be a diaphragm pump, e.g. preferably a smallportable diaphragm pump. This is a preferred type of pump, in order inparticular to reduce or eliminate contact of internal surfaces andmoving parts of the pump with (chronic) wound exudate, and for ease ofcleaning.

Where the pump is a diaphragm pump, and preferably a small portablediaphragm pump, the one or two flexible diaphragms that displace liquidmay each be, for example a polymer film, sheet or membrane, that isconnected to means for creating the pulsations. This may be provided inany form that is convenient, inter alia as a piezoelectric transducer, acore of a solenoid or a ferromagnetic integer and coil in which thedirection of current flow alternates, a rotary cam and follower, and soon.

Where any second device is applied to the fluid in the fluid supply tubeupstream of and towards the wound dressing, it will usually applypositive pressure (i.e. above-atmospheric pressure) to the wound bed.

As with the (first) device, it may be a fixed-throughput device, such asa fixed-speed pump, which will usually require a discrete means forsupply flow regulation, connected to a fluid supply tube, e.g. aregulator, such as a rotary valve.

Alternatively, where appropriate the second device for moving irrigantfluid to the wound may be a variable-throughput device, such as avariable speed pump, upstream of the wound dressing, thus effectivelyforming a combination of a second device for moving fluid through thewound with means for supply flow regulation in a single integer.

The second device for moving fluid through the wound will often be apump of any of the following types applied to the irrigant in the fluidsupply tube upstream of and towards the wound dressing. It may be afixed-speed pump, with (as above) a discrete means for supply flowregulation, connected to a fluid supply tube, e.g. a regulator, such asa rotary valve. Alternatively, where appropriate the pump may be avariable-throughput or variable-speed pump.

The following types of pump may be used as the second device:

-   -   Reciprocating Pumps, such as        -   Shuttle Pumps—with an oscillating shuttle mechanism to move            fluids at rates from 2 to 50 ml per minute and    -   Rotary Pumps, such as:        -   Centrifugal Pumps        -   Flexible Impeller    -   Pumps—where elastomeric impeller traps fluid between impeller        blades and a moulded housing that sweeps fluid through the pump        housing.    -   Peristaltic Pumps—with peripheral rollers on rotor arms acting        on a flexible fluid aspiration tube to urge fluid current flow        in the tube in the direction of the rotor.    -   Rotary Vane Pumps—with rotating vaned disk attached to a drive        shaft moving fluid without pulsation as it spins. The outlet can        be restricted without damaging the pump.

The second device may be a peristaltic pump, e.g. preferably a smallportable peristaltic pump. This is a preferred type of pump, in order inparticular to reduce or eliminate contact of internal surfaces andmoving parts of the pump with irrigant, and for ease of cleaning.

Where the pump is a peristaltic pump, this may be e.g. an Instech ModelP720 miniature peristaltic pump, with a flow rate: of 0.2-180 ml/hr anda weight of <0.5 k. This is potentially useful for home and fieldhospital use.

Each such pump of any these types may also suitably be one that iscapable of pulsed, continuous, variable and/or automated and/orprogrammable fluid movement. Less usually and less preferably, each suchpump of any these types will be reversible.

As above, the means for supply flow regulation may be a regulator, suchas a rotary valve. This is connected between two parts of a fluid supplytube, such that the desired supply flow regulation is achieved.

If there are two or more inlet pipes, these may be connected to a singlefluid supply tube with a single regulator, or to first, second, etc.fluid supply tubes, respectively having a first regulator, a secondregulator, etc., e.g. a valve or other control device for admittingfluids into the wound.

As above, the means for aspirate flow regulation may be similarlyprovided in a form in which concomitant aspirate flow regulation ispossible. It may be a regulator, such as a valve or other controldevice, e.g. a rotary valve.

Multiple offtake tubes may be similarly provided with single or multipleregulators, all for aspiration of fluids from the apparatus, e.g. to aaspirate collection vessel, such as a collection bag.

If there is no second device for moving fluid through the wound appliedto the irrigant in the fluid supply tube upstream of and towards thewound dressing, it is only possible to apply a negative pressure to thewound, by means of the device for moving fluid through the wound appliedto the aspirate in the fluid offtake tube downstream of and away fromthe wound dressing.

Operation may e.g. be carried out at a negative pressure of up to 50%atm., typically at a low negative pressure of up to 20% atm., moreusually up to 10% atm. at the wound, as is described hereinafter.

Examples of suitable and preferred (first) devices include those typesof pump that are so described hereinbefore in relation to the firstdevice. This may be a diaphragm pump, e.g. preferably a small portablediaphragm pump. This is a preferred type of pump, in order in particularto reduce or eliminate contact of internal surfaces and moving parts ofthe pump with (chronic) wound exudate, and for ease of cleaning.

Alternatively, if it is desired to apply a net positive pressure to thewound, the means for providing simultaneous aspiration and irrigation ofthe wound must comprise not only a first device for moving fluid throughthe wound applied to the aspirate in the fluid offtake tube downstreamof and away from the wound dressing, but also a second device for movingfluid through the wound applied to the irrigant in the fluid supply tubeupstream of and towards the wound dressing.

Operation may then e.g. be carried out at a positive pressure of up to50% atm., typically at a low positive pressure of up to 20% atm., moreusually up to 10% atm. at the wound, as is described hereinafter.

Examples of suitable and preferred first devices include those types ofpump that are so described hereinbefore in relation to the first device.This may be a diaphragm pump, e.g. preferably a small portable diaphragmpump.

This is a preferred type of pump, in order in particular to reduce oreliminate contact of internal surfaces and moving parts of the pump with(chronic) wound exudate, and for ease of cleaning.

Examples of suitable and preferred second devices include those types ofpump that are so described hereinbefore in relation to the seconddevice. This may be a peristaltic pump, e.g. a miniature peristalticpump.

This is a preferred type of pump, in order to eliminate contact ofinternal surfaces and moving parts of the pump with irrigant in thefluid supply tube upstream of and towards the wound dressing, and forease of cleaning.

It is of course equally possible to apply a negative pressure to thewound, by means of such a combination of a first device for moving fluidthrough the wound applied to the aspirate in the fluid offtake tubedownstream of and away from the wound dressing, and a second device formoving fluid through the wound applied to the irrigant in the fluidsupply tube upstream of and towards the wound dressing; optionally withmeans for supply flow regulation, connected to a fluid supply tube;and/or means for aspirate flow regulation, connected to a fluid offtaketube.

Indeed, as noted below in this regard, preferred embodiments of theapparatus of this first aspect of the present invention for aspirating,irrigating and/or cleansing chronic wounds that apply a negativepressure include such types of combination of; a first device, e.g. adiaphragm pump, e.g. preferably a small portable diaphragm pump, and asecond device, e.g. a peristaltic pump, preferably a miniatureperistaltic pump,

As noted above, either of the first device and the second device may bea fixed-throughput device, such as a fixed-speed pump, which willusually require a discrete means for aspirate flow regulation, connectedto a fluid offtake tube, and/or means for supply flow regulation,connected to a fluid supply tube, in each case, e.g. a regulator, suchas a rotary valve, or a variable-throughput device, such as avariable-speed pump, downstream of the wound dressing, thus effectivelyforming a combination of a (first) device for moving fluid through thewound with means for aspirate flow regulation and/or means for supplyflow regulation in a single integer. The higher end of the ranges of %positive and negative pressure noted above—are potentially more suitablefor hospital use, where they may only be used safely under professionalsupervision.

The lower end is potentially more suitable for home use, whererelatively high % positive and negative pressures cannot be used safelywithout professional supervision, or for field hospital use.

In each case, the pressure on the wound may be held constant throughoutthe desired length of therapy, or may be varied cyclically in a desiredpositive or negative pressure regime.

As noted above, when it is desired to apply a negative pressure to thewound, it is preferred that the means for providing simultaneousaspiration and irrigation of the wound comprise not only a (first)device for moving fluid through the wound applied to the aspirate in thefluid offtake tube downstream of and away from the wound dressing, butalso a second device for moving fluid through the wound applied to theirrigant in the fluid supply tube upstream of and towards the wounddressing.

Accordingly, one embodiment of the apparatus for irrigating, cleansingand/or aspirating wounds of the present invention is characterized inthe means for providing simultaneous aspiration and irrigation of thewound comprises: a (first) device for moving fluid through the woundapplied to fluid downstream of and away from the wound dressing, and asecond device for moving fluid through the wound applied to the irrigantin the fluid supply tube upstream of and towards the wound dressing; incombination with at least one of means for supply flow regulation,connected to a fluid supply tube; and means for aspirate flowregulation, connected to a fluid offtake tube.

As noted above, either of the first device and the second device may bea fixed-throughput device, such as a fixed-speed pump, which willusually require a discrete means for aspirate flow regulation, connectedto a fluid offtake tube, and/or means for supply flow regulation,connected to a fluid supply tube, in each case, e.g. a regulator, suchas a rotary valve, or a variable-throughput device, such as avariable-speed pump, downstream of the wound dressing, thus effectivelyforming a combination of a (first) device for moving fluid through thewound with means for aspirate flow regulation and/or means for supplyflow regulation in a single integer.

This combination of a) a device for moving fluid through the woundapplied to the aspirate in the fluid offtake tube downstream of and awayfrom the wound dressing, and b) a device for moving fluid through thewound applied to the fluid in the fluid supply tube upstream of andtowards the wound dressing, may be used to apply an overall positive ornegative, or even zero pressure to the wound.

At least one body in the flow path to, over and from the wound bedshould have sufficient resilience against the pressure to allow anysignificant compression or decompression of the fluid occur.

Thus, examples of suitable bodies include those which are or are definedby a film, sheet or membrane, such as inlet or offtake and/or tubes andstructures such as bags, chambers and pouches, filled with irrigantfluid, and e.g. the backing layer of the wound dressing, made ofelastically resilient thermoplastic materials.

It will be seen that the balance of fluid between aspirated fluid fromthe wound and irrigant supplied to the wound from the fluid reservoirwill thus be largely determined by a means for providing simultaneousaspiration and irrigation of the wound which is a system comprising: a)means for aspirate flow regulation and/or a device for moving fluidthrough the wound applied to fluid downstream of and away from the wounddressing, and b) means for supply flow regulation and/or a device formoving fluid through the wound applied to the fluid in the fluid supplytube upstream of and towards the wound dressing.

The same means may be used to apply an overall positive or negative, oreven neutral pressure to the wound.

The appropriate flow rate through the supply tube will depend on anumber of factors, such as:

-   -   the viscosity and consistency of each of the irrigant, exudate        and mixed exudate-irrigant fluid, and any changes as the wound        heals;    -   the level of negative pressure on the wound bed, whether the        irrigant in the fluid supply tube upstream of and into the wound        dressing is under positive pressure, and the level of such        pressure;    -   the level of any pressure drop between the irrigant in the fluid        supply tube upstream of the wound dressing and the wound bed,        such as across a porous element, e.g. a membrane wound contact        layer on the lower surface of an inlet manifold that delivers        the fluid directly to the wound bed;    -   means for supply flow regulation;    -   and/or a second device for moving fluid through the wound        applied to the fluid in the fluid supply tube upstream of and        towards the wound dressing;    -   the depth and/or capacity of the wound and the power consumption        needed for a given desired fluid volume flow rate of irrigant        and/or wound exudate through the wound.

The dressing may comprise an inlet manifold (as described in furtherdetail hereinafter) that generally covers and contacts a significantarea, preferably most, of the wound bed with openings that deliver thefluid directly to the wound bed over an extended area, in the form ofone or more inflatable hollow bodies defined by a film sheet ormembrane. The (usually small) positive pressure above atmospheric fromthe irrigation device when both devices are running together should besufficient to inflate the manifold.

The desired fluid volume flow rate of irrigant and/or wound exudate ispreferably that for optimum performance of the wound healing process.

The flow rate will usually be in the range of 1 to 1500 ml/hr, such as 5to 1000 ml/hr, e.g. 15 to 300 ml/hr, such as 35 to 200 ml/hr through thesupply tube. The flow rate through the wound may be held constantthroughout the desired length of therapy, or may be varied cyclically ina desired flow rate regime.

In practice, the offtake rate of flow of total irrigant and/or woundexudate will generally be of the order of 1 to 2000, e.g. 35 to 300ml/24 hr/cm², where the cm² refers to the wound area, depending onwhether the wound is in a highly exuding state.

In practice, the rate of exudate flow is typically only of the order ofup to 75 microlitres/cm²/hr (where cm² refers to the wound area), andthe fluid can be highly mobile or not, depending on the level ofproteases present). Exudate levels drop and consistency changes as thewound heals, e.g. to a level for the same wound that equates to 12.5-25microlitres/cm²/hr.

It will be apparent that the aspirated fluid from the wound willtypically contain a preponderance of irrigant from the fluid reservoirover wound exudate.

The necessary adjustments to maintain the desired balance of fluid bymeans of a) the means for aspirate flow regulation and/or downstreamdevice, and b) the means for supply flow regulation and/or upstreamdevice for moving fluid will be apparent to the skilled person, bearingin mind that, as noted above, either of the first device and the seconddevice may be:

-   -   a fixed-throughput device, such as a fixed-speed pump, which        will usually require a discrete means for aspirate flow        regulation, connected to a fluid offtake tube, and/or means for        supply flow regulation, connected to a fluid supply tube, in        each case, e.g. a regulator, such as a rotary valve, or    -   a variable-throughput device, such as a variable-speed pump,        downstream of the wound dressing, thus effectively forming a        combination of a (first) device for moving fluid through the        wound with means for aspirate flow regulation and/or means for        supply flow regulation in a single integer.

The type and/or capacity of a suitable second device will be largelydetermined by a) the appropriate or desired fluid volume flow rate ofirrigant and/or wound exudate from the wound, and b) whether it isappropriate or desired to apply a positive or negative pressure to thewound bed, and the level of such pressure to the wound bed for optimumperformance of the wound healing process, and by factors such asportability, power consumption and isolation from contamination.

As noted above, when it is desired to apply a negative pressure to thewound with the apparatus of the present invention for aspirating,irrigating and/or cleansing wounds to provide simultaneous aspirationand irrigation of the wound, the means for providing simultaneousaspiration and irrigation of the wound may comprise a single device formoving fluid through the wound applied to the aspirate in the fluidofftake tube downstream of and away from the wound dressing or incombination with at least one of means for supply flow regulation,connected to a fluid supply tube, and means for aspirate flowregulation, connected to a fluid offtake tube.

As noted above, the device may be a fixed-throughput device, or avariable throughput device.

It should be noted that such an apparatus as described above will begenerally suitable for sequential irrigation/aspiration.

In a further aspect the present invention provides a method of operationof an apparatus for aspirating, irrigating and/or cleansing wounds, saidmethod comprising the steps of: a) providing an apparatus as set outabove b) applying the wound dressing to the wound c) conforming thebacking layer of the wound dressing to the shape of the bodily part inwhich the wound is to form a relatively fluid tight seal or closure; d)activating at least one device for moving fluid through the wounddressing to the wound and/or from the wound to course irrigant to moveto the wound; e) activating means for applying high frequencyvibrational energy to the wound bed.

In a preferred embodiment the apparatus has at least one inlet pipe andat least one outlet pipe, each of which passes through and/or under thewound-facing face. Such an embodiment allows for a method ofsimultaneous and/or sequential irrigation/aspiration of the wound. Insuch an embodiment step d) of the method comprises activating at leastone device for moving through the wound dressing to move fluid(irrigant) through the at least one inlet and to move fluid (aspirate)out of the at least one output pipe.

In a preferred embodiment the irrigant is moved to the wound via theoutlet pipe and the aspirate removed via the outlet pipe.simultaneously, i.e. simultaneous aspiration/irrigation. This may becarried out for substantially the entirety of the treatment of thewound, or alternatively for portions of the treatment as desired.

Such an embodiment is also suitable for sequential (fill/empty)operation, and thus a method wherein sequential operation is carried outforms an alternative embodiment of the invention. In such an embodimentirrigation would be ceased by ceasing the device moving fluid throughthe at least one inlet and activating a device to move fluid from thewound through the outlet.

Suitable flow rates, parameters for operation of the means for applyingstress and for operation of the apparatus in general are set out above.Further details are given below.

The operation of a typical apparatus of this type for simultaneousaspiration and irrigation of a wound at a low negative pressure of up to20% atm., more usually up to 10% atm. at the wound, with one pump mayinvolve the following. As mentioned previously the application ofnegative pressure has beneficial effects in wound healing.

Before starting the apparatus of this first aspect of the presentinvention for aspirating, irrigating and/or cleansing wounds, thebacking layer of the wound dressing is applied over the wound andconformed to the shape of the bodily part in which the wound is to forma relatively fluid-tight seal or closure.

The means for supply flow regulation, connected to a fluid supply tube,such as a regulator, such as a rotary valve, is usually closed, and themeans for aspirate flow regulation (if any), connected to a fluidofftake tube, is opened.

The aspiration pump is started and run to give a negative pressure of upto 50% atm., more usually up to 20% atm., e.g. up to 10% atm. to beapplied to the interior of the dressing and the wound.

The means for fluid supply regulation is opened and is then adjusted,and/or where the aspiration pump is a variable-speed pump, downstream ofthe wound dressing, that is adjusted, to maintain the desired balance offluid at a controlled nominal flow rate and to maintain the desirednegative pressure in the interior of the wound dressing.

The means for applying high frequency vibrational energy to the woundbed is then activated. Further details of this means and its operationare given above. The means may be activated continuously or intermittedas desired.

The apparatus is then run for the desired length of therapy and with thedesired negative pressure regime and with application of the highfrequency vibrational energy regime as desired.

After this period, the aspiration pump is stopped.

The operation of a typical apparatus for simultaneous aspiration andirrigation of a wound at a low negative pressure of up to 20% atm., moreusually up to 10% atm. at the wound, with two pumps may involve thefollowing steps.

The necessary changes where the mode of operation is at a net positivepressure of e.g. up to 15% atm., more usually up to 10% atm. at thewound will be apparent to the skilled person.

Such a typical apparatus for simultaneous aspiration and irrigation of awound at a low negative pressure of up to 20% atm., more usually up to10% atm. at the wound comprises means for Providing simultaneousaspiration and irrigation of the wound which is a combination of a) afirst device for moving fluid through the wound applied to the aspiratein the fluid offtake tube downstream of and away from the wounddressing, with optional means for aspirate flow regulation, connected toa fluid offtake tube: and b) a second device for moving fluid throughthe wound applied to the irrigant in the fluid supply tube upstream ofand towards the wound dressing, with optional means for supply flowregulation, connected to a fluid supply tube.

As noted above, either device may be a fixed-throughput device orvariable throughput device.

Before starting the apparatus of this first aspect of the presentinvention for aspirating, irrigating and/or cleansing wounds, thebacking layer of the wound dressing is applied over the wound andconformed to the shape of the bodily part in which the wound is to forma relatively fluid-tight seal or closure.

Any means for supply flow regulation, connected to a fluid supply tube,such as a regulator; such as a rotary valve, is usually closed, and anymeans for aspirate flow regulation, connected to a fluid offtake tube,is opened.

The aspiration pump is started and run to apply a negative pressure ofup to 50% atm., more usually up to 20% atm., e.g. up to 10% atm., to theinterior of the dressing and the wound.

The irrigation pump is then started, so that both pumps are runningtogether, and any means for supply flow regulation is opened.

The irrigation pump flow rate and any means for fluid supply regulationare then adjusted and/or where the aspiration pump and/or the irrigationpump is a variable-speed pump, either or both is/are is adjusted, tomaintain the desired balance of fluid at a controlled nominal flow rateand to maintain the desired negative pressure in the interior of thewound dressing.

The means for applying high frequency vibrational energy is thenactivated, as discussed previously.

The apparatus is then run for the desired length of therapy and with thedesired pressure regime and high frequency vibrational energy regime.

After this period, the irrigation pump is stopped, shortly followed bythe aspiration pump.

In all embodiments of the apparatus of this first aspect of the presentinvention for aspirating, irrigating and/or cleansing wounds, aparticular advantage is the tendency of the wound dressing to conform tothe shape of the bodily part to which it is applied.

The term ‘relatively fluid-tight seal or closure’ is used herein toindicate one which is fluid- and microbe-impermeable and permits apositive or negative pressure of up to 50% atm., more usually up to 20%atm., e.g. up to 10% atm. to be applied to the wound. The term ‘fluid’is used herein to include gels, e.g. thick exudate, liquids, e.g. water,and gases, such as air, nitrogen, etc.

The shape of the backing layer that is applied may be any that isappropriate to aspirating, irrigating and/or cleansing the wound acrossthe area of the wound.

Examples of such include a substantially flat film, sheet or membrane,or a bag, chamber, pouch or other structure of the backing layer, e.g.of polymer film, which can contain the fluid.

The backing layer may be a film, sheet or membrane, often with a(generally uniform) thickness of up to 100 micron, preferably up to 50micron, more preferably up to 25 micron, and of 10 micron minimumthickness.

Its largest cross-dimension may be up to 500 mm (for example for largetorso wounds), up to 100 mm (for example for axillary and inguinalwounds), and up to 200 mm for limb wounds (for example for chronicwounds, such as venous leg ulcers and diabetic foot ulcers.

Desirably the dressing is resiliently deformable, since this may resultin increased patient comfort, and lessen the risk of inflammation of awound.

Suitable materials for it include synthetic polymeric materials that donot absorb aqueous fluids, such as polyolefins, such as polyethylenee.g. high density polyethylene, polypropylene, copolymers thereof, forexample with vinyl acetate and polyvinyl alcohol, and mixtures thereof;polysiloxanes; polyesters, such as polycarbonates; polyamides, e.g. 6-6and 6-10, and hydrophobic polyurethanes.

They may be hydrophilic, and thus also include hydrophilicpolyurethanes.

They also include thermoplastic elastomers and elastomer blends, forexample copolymers, such as ethyl vinyl acetate, optionally or asnecessary blended with high-impact polystyrene.

They further include elastomeric polyurethane, particularly polyurethaneformed by solution casting.

Preferred materials for the present wound dressing include thermoplasticelastomers and curable systems.

The backing layer is capable of forming a relatively fluid-tight seal orclosure over the wound and/or around the inlet and outlet pipe(s).

However, in particular around the periphery of the wound dressing,outside the relatively fluid-tight seal, it is preferably of a materialthat has a high moisture vapour permeability, to prevent maceration ofthe skin around the wound. It may also be a switchable material that hasa higher moisture vapour permeability when in contact with liquids, e.g.water, blood or wound exudate. This may, e.g. be a material that is usedin Smith & Nephew's Allevyn™, IV3000™ and OpSite™ dressings.

The periphery of the wound-facing face of the backing layer may bear anadhesive film, for example, to attach it to the skin around the wound.This may, e.g. be a pressure-sensitive adhesive, if that is sufficientto hold the wound dressing in place in a fluid-tight seal around theperiphery of the wound-facing face of the wound dressing.

Alternatively or additionally, where appropriate a light switchableadhesive could be used to secure the dressing in place to preventleakage. (A light switchable adhesive is one the adhesion of which isreduced by photocuring. Its use can be beneficial in reducing the traumaof removal of the dressing.)

Thus, the backing layer may have a flange or lip extending around theproximal face of the backing layer, of a transparent or translucentmaterial (for which it will be understood that materials that are listedabove are amongst those that are suitable). This bears a film of a lightswitchable adhesive to secure the dressing in place to prevent leakageon its proximal face, and a layer of opaque material on its distal face.

To remove the dressing and not cause excessive trauma in removal of thedressing, the layer of opaque material on the distal face of the flangeor lip extending around the proximal wound is removed prior toapplication of radiation of an appropriate wavelength to the flange orlip.

If the periphery of the wound dressing, outside the relativelyfluid-tight seal, that bears an adhesive film to attach it to the skinaround the wound, is of a material that has a high moisture vapourpermeability or is a switchable material, then the adhesive film, ifcontinuous, should also have a high or switchable moisture vapourpermeability, e.g. be an adhesive such as used in Smith & Nephew'sAllevyn™, IV3000™ and OpSite™ dressings. Where a vacuum, is applied tohold the wound dressing in place in a fluid tight seal around theperiphery of the wound-facing face of the wound dressing, the wounddressing may be provided with a silicone flange or lip to seal thedressing around the wound. This removes the need for adhesives andassociated trauma to the patient's skin. Where the interior of, and theflow of irrigant and/or wound exudate to and through, the dressing isunder any significant positive pressure, which will tend to act atperipheral points to lift and remove the dressing off the skin aroundthe wound.

In such use of the apparatus, it may thus be necessary to providesecuring means for forming and maintaining such a seal or closure overthe wound against such positive pressure on the wound, to act atperipheral points for this purpose. Examples of such securing meansinclude light switchable adhesives, as above, to secure the dressing inplace to prevent leakage. Since the adhesion of a light switchableadhesive is reduced by photocuring, thereby reducing the trauma ofremoval of the dressing, a film of a more aggressive adhesive may beused, e.g. on a flange, as above.

Examples of suitable fluid adhesives for use in more extreme conditionswhere trauma to the patient's skin is tolerable include ones thatconsist essentially of cyanoacrylate and like tissue adhesives, appliedaround the edges of the wound and/or the proximal face of the backinglayer of the wound dressing, e.g. on a flange or lip.

Further suitable examples of such securing means include adhesive (e.g.with pressure-sensitive adhesive) and non-adhesive, and elastic andnonelastic straps, bands, loops, strips, ties, bandages, e.g.compression bandages, sheets, covers, sleeves, jackets, sheathes, wraps,stockings and hose, e.g. elastic tubular hose or elastic tubularstockings that are a compressive fit over a limb wound to apply suitablepressure to it when the therapy is applied in this way; and inflatablecuffs, sleeves, jackets, trousers, sheathes, wraps, stockings and hosethat are a compressive fit over a limb wound to apply suitable pressureto it when the therapy is applied in this way.

Such securing means may each be laid out over the wound dressing toextend beyond the periphery of the backing layer of the wound dressing,and as appropriate will be adhered or otherwise secured to the skinaround the wound and/or itself and as appropriate will apply compression(e.g. with elastic bandages, stockings) to a degree that is sufficientto hold the wound dressing in place in a fluid-tight seal around theperiphery of the wound,

Such securing means may each be integral with the other components ofthe dressing, in particular the backing layer.

Alternatively, it may be permanently attached or releasably attached tothe dressing, in particular the backing layer, with an adhesive film,for example, or these components may be a Velcro™, push snap ortwist-lock fit with each other.

The securing means and the dressing may be separate structures,permanently unattached to each other.

In a more suitable layout for higher positive pressures on the wound, astiff flange or lip extends around the periphery of the proximal face ofthe backing layer of the wound dressing as hereinbefore defined. Theflange or lip is concave on its proximal face to define a peripheralchannel or conduit. It has a suction outlet that passes through theflange or lip to communicate with the channel or conduit and may beconnected to a device for applying a vacuum, such as a pump or a pipedsupply of vacuum.

The backing layer may be integral with or attached, for example by heatsealing, to the flange or lip extending around its proximal face.

To form the relatively fluid-tight seal or closure over a wound that isneeded and to prevent passage of irrigant and/or exudate under theperiphery of the wound-facing face of the wound dressing, in use of theapparatus, the dressing is set on the skin around the wound. The devicethen applies a vacuum to the interior of the flange or lip, thus formingand maintaining a seal or closure acting at peripheral points around thewound against the positive pressure on the wound.

With all the foregoing means of attachment, and means for forming andmaintaining a seal or closure over the wound, against positive ornegative pressure on the wound at peripheral points around the wound,the wound dressing sealing periphery is preferably of a generally roundshape, such as an ellipse, and in particular circular.

To form the relatively fluid-tight seal or closure over a wound andaround the inlet pipe(s) and outlet pipe(s) at the point at which theypass through and/or under the wound-facing face, the backing layer maybe integral with these other components.

The components may alternatively just be a push, snap or twist-lock fitwith each other, or adhered or heat-sealed together.

The or each inlet pipe or outlet pipe may be in the form of an aperture,such as a funnel, hole, opening, orifice, luer, slot or port forconnection as a female member respectively to a mating end of a fluidtube and/or fluid supply tube (optionally or as necessary via means forforming a tube, pipe or hose, or nozzle, hole, opening, orifice, luer,slot or port for connection as a male member respectively to a matingend of a fluid tube and/or fluid supply tube (optionally or as necessaryvia means for supply flow regulation) or a fluid offtake tube.

Where the components are integral they will usually be made of the samematerial (for which it will be understood that materials that are listedabove are amongst those that are suitable).

Where, alternatively, they are a push, snap or twist-lock fit, the maybe of the same material or of different materials. In either case,materials that are listed above are amongst those that are suitable forall the components.

The or each pipe will generally pass through, rather than under thebacking layer. In such case, the backing layer may often have a rigidand/or resiliently inflexible or stiff area to resist any substantialplay between the or each pipe and the or each mating tube, ordeformation under pressure in any direction.

It may often be stiffened, reinforced or otherwise strengthened by aboss projecting distally (outwardly from the wound) around each relevanttube, pipe or hose, or nozzle, hole, opening, orifice, luer, slot orport for connection to a mating end of a fluid tube and/or fluid supplytube or fluid offtake tube.

Alternatively or additionally, where appropriate the backing layer mayhave a stiff flange or lip extending around the proximal face of thebacking layer to stiffen, reinforce or otherwise strengthen the backinglayer.

Where a simple pipe is used to supply the irrigant to the wound, thismay not provide a system to distribute irrigant over a sufficientfunctional surface area to irrigate the wound at a practical rate to besuitable for use, in particular in chronic wound aspiration andirrigation, which may contain relatively high concentrations ofmaterials that are deleterious to wound healing.

It may be advantageous to provide a system where wound irrigant may bedistributed more evenly, or pass in a more convoluted path under thedressing over the wound bed.

Accordingly, one form of the dressing is provided with a ‘tree’ form ofpipes, tubes or tubules that radiate from an inlet manifold to the woundbed to end in apertures and deliver the aspirating fluid directly to thewound bed via the apertures. Similarly, there is optionally an outletmanifold from which tubules radiate and run to the wound bed to end inopenings and collect the fluid directly from the wound bed.

The pipes, etc. may radiate regularly or irregularly through the woundin use, respectively from the inlet or outlet manifold, althoughregularly may be preferred. A more suitable layout for deeper wounds isone in which the pipes, etc. radiate hemispherically and concentrically,to the wound bed.

For shallower wounds, examples of suitable forms of such layout of thepipes, etc. include ones in which the pipes, etc. radiate in a flattenedhemiellipsoid and concentrically, to the wound bed. Other suitable formsof layout of the pipes, etc. include one which have pipes, tubes ortubules extending from the inlet pipe(s) and/or outlet pipe(s) at thepoint at which they pass through and/or under the wound-facing face ofthe backing layer to run over the wound bed. These may have a blind borewith perforations, apertures, holes, openings, orifices, slits or slotsalong the pipes, etc.

These pipes, etc. then effectively form an inlet pipe manifold thatdelivers the aspirating fluid directly to the wound bed or outlet pipeor collects the fluid directly from the wound respectively. It does sovia the holes, openings, orifices, slits or slots in the tubes, pipes,tubules, etc. over most of the wound bed under the backing layer.

It may be desirable that the tubes, pipes or tubules are resilientlyflexible, e.g. elastomeric, and preferably soft, structures with goodconformability in the wound and the interior of the wound dressing.

When the therapy is applied in this way, the layout of the tubes, pipes,tubules, etc. may depend on the depth and/or capacity of the wound.

Thus, for shallower wounds, examples of suitable forms of such layout ofthe tubes, pipes, tubules, etc. include ones that consist essentially ofone or more of the tubes, etc. in a spiral.

A more suitable layout for deeper wounds when the therapy is applied inthis way may be one which comprises one or more of the tubes, etc. in ahelix or spiral helix.

Other suitable layouts for shallower wounds include one which haveblindbore, perforated inlet pipe or outlet pipe manifolds that aspiratefluid in the wound when the dressing is in use.

One or both of these may be such a form, the other may be, e.g. one ormore straight blind-bore, perforated radial tubes, pipes or nozzles.

A preferred form of inlet pipe (or less usually outlet pipe) manifoldthat delivers the aspirating fluid directly to the wound bed or collectsthe fluid directly from the wound respectively is one that comprise oneor more conformable hollow bodies defined by a film, sheet or membrane,such as a bag, chamber, pouch or other structure, filled with theirrigant (or less usually) aspirate from the wound, passing throughperforations, apertures, holes, openings, orifices, slits or slots inthe film, sheet or membrane defining the hollow body or hollow bodies.

These may be of small cross-dimension, so that they may then effectivelyform microperforations, microapertures or pores in a permeable integer,for example the polymer film, sheet or membrane.

This type of manifold for irrigation (more usually) provides the highestuniformity in the flow distribution of irrigant over the wound at apractical rate to be suitable for use, in particular in chronic woundaspiration and irrigation, and hence to provide a system where materialsthat are beneficial in promoting wound healing, such as growth factors,cell matrix components, and other physiologically active components ofthe exudate from a wound, are distributed more evenly under the dressingover the wound bed.

This type of manifold for irrigation (more usually) is noted below withregard to wound fillers under the backing layer, since it is aresiliently flexible, e.g. elastomeric, and soft, structure with goodconformability to wound shape. It is urged by its own resilience againstthe backing layer to apply gentle pressure on the wound bed, and istherefore also capable of acting as a wound filler. The film, sheet ormembrane, often has a (generally uniform) thickness similar to that offilms or sheets used in conventional wound dressing backing layers.

Another suitable layout is one in which an inlet pipe and/or outlet pipemanifold that delivers the aspirating fluid directly to the wound bed orcollects the fluid directly from the wound respectively via inlet and/oroutlet tubes, pipes or tubules, and the inlet manifold and/or outletmanifold is formed by slots in layers permanently attached to each otherin a stack, and the inlet and/or outlet tubes, pipes or tubules areformed by apertures through layers permanently attached to each other ina stack. (In FIG. 10 a there is shown an exploded isometric view of sucha stack, which is non-limiting.)

As also mentioned herein, the backing layer that is applied may be anythat is appropriate to the present system of therapy and permits apositive or negative pressure of up to 50% atm., more usually up to 25%atm. to be applied to the wound.

It is thus often a microbe-impermeable film, sheet or membrane, which issubstantially flat, depending on any pressure differential on it, andoften with a (generally uniform) thickness similar to such films orsheets used in conventional wound dressings, i.e. up to 100 micron,preferably up to 50 micron, more preferably up to 25 micron, and of 10micron minimum thickness.

The backing layer may often have a rigid and/or resiliently inflexibleor stiff area to resist any substantial play between other componentsthat are not mutually integral, and may be stiffened, reinforced orotherwise strengthened, e.g. by a projecting boss.

Such a form of dressing would not be very conformable to the wound bed,and may effectively form a chamber, hollow or cavity defined by abacking layer and the wound bed under the backing layer. It may bedesirable that the interior of the wound dressing conform to the woundbed, even for a wound in a highly exuding state. Accordingly, one formof the dressing is provided with a wound filler under the backing layer.

This is favourably a resiliently flexible, e.g. elastomeric, andpreferably soft, structure with good conformability to wound shape. Itis urged by its own resilience against the backing layer to apply gentlepressure on the wound bed. The wound filler may be integral with theother components of the dressing, in particular the backing layer.

Alternatively, it may be permanently attached to them/it, with anadhesive film, for example, or by heat-sealing, e.g. to a flange or lipextending from the proximal face, so a not to disrupt the relativelyfluid-tight seal or closure over the wound that is needed.

Less usually, the wound filler is releasably attached to the backinglayer, with an adhesive film, for example, or these components may be apush, snap or twist-lock fit with each other.

The wound filler and the backing layer may be separate structures,permanently unattached to each other.

The wound filler may be or comprise a solid integer, favourably aresiliently flexible, e.g. elastomeric, and preferably soft, structurewith good conformability to wound shape. Examples of suitable forms ofsuch wound fillers are foams formed of a suitable material, e.g. aresilient thermoplastic.

Preferred materials for the present fillers include reticulatedfiltration polyurethane foams with small apertures or pores.

Alternatively or additionally, it may be in the form of, or comprise oneor more conformable hollow bodies defined by a film, sheet or membrane,such as a bag, chamber, pouch or other structure, filled with a fluid orsolid that urges it to the wound shape.

The film, sheet or membrane, often has a (generally uniform) thicknesssimilar to that of films or sheets used in conventional wound dressingbacking layers.

That is, up to 100 micron, preferably up to 50 micron, more preferablyup to 25 micron, and of 10 micron minimum thickness, and is oftenresiliently flexible, e.g. elastomeric, and preferably soft.

Such a filler is often integral with the other components of thedressing, in particular the backing layer, or permanently attached tothem/it, with an adhesive film, for example, or by heat-sealing, e.g. toa flange Examples of suitable fluids contained in the hollow body orbodies defined by a film, sheet or membrane include gases, such as air,nitrogen and argon, more usually air, at a small positive pressure aboveatmospheric; and liquids, such as water, saline.

Examples also include gels, such as silicone gels, e.g. CaviCare™ gel,or preferably cellulosic gels, for example hydrophilic cross-linkedcellulosic gels, such as Intrasite™ cross-linked materials.

Examples also include aerosol foams, where the gaseous phase of theaerosol system is air or an inert gas, such as nitrogen or argon, moreusually air, at a small positive pressure above atmospheric; and solidparticulates, such as plastics crumbs.

Of course, if the backing layer is a sufficiently conformable and/ore.g. an upwardly dished sheet, the backing layer may lie under the woundfiller, rather than vice versa.

In this type of layout, in order for the wound filler to urge the wounddressing towards the wound bed, it will usually have to be firmlyadhered or otherwise releasably attached to the skin around the wound.This is especially the case in those embodiments where the wound fillerand the backing layer are separate structures, permanently unattached toeach other.

In such a layout for deeper wounds when the therapy is applied in thisway, the means for such attachment may also form and maintain a seal orclosure over the wound.

Where the filler is over the backing layer, and the fluid inlet pipe(s)and outlet pipe(s) pass through the wound-facing face of the backinglayer, they may run through or around the wound filler over the backinglayer. One form of the dressing is provided with a wound filler underthe backing layer that is or comprises a resiliently flexible, e.g.elastomeric, and preferably soft, hollow body defined by a film, sheetor membrane, such as a bag, chamber, pouch or other structure.

It has apertures, holes, openings, orifices, slits or slots, or tubes,pipes, tubules or nozzles. It communicates with at least one inlet oroutlet pipe through at least one aperture, hole, opening, orifice, slitor slot.

The fluid contained in the hollow body may then be the aspirating orirrigating fluid in the apparatus.

The hollow body or each of the hollow bodies then effectively forms aninlet pipe or outlet pipe manifold that delivers the aspirating fluiddirectly to the wound bed or collects the fluid directly from the woundrespectively via the holes, openings, orifices, slits or slots, or thetubes, pipes or hoses, etc. in the film, sheet or membrane.

When the therapy is applied in this way, the type of the filler may alsobe largely determined by the depth and/or capacity of the wound.

Thus, for shallower wounds, examples of suitable wound fillers as acomponent of a wound dressing include ones that consist essentially ofone or more conformable hollow bodies defining an inlet pipe and/oroutlet pipe manifold that delivers the aspirating fluid directly to thewound bed or collects the fluid directly from the wound.

A more suitable wound filler for deeper wounds when the therapy isapplied in this way may be one which comprises one or more conformablehollow bodies defined by, for example a polymer film, sheet or membrane,that at least partly surround(s) a solid integer. This may provide asystem with better rigidity for convenient handling.

The wound filler under the backing layer may effectively form (or beformed by) an inlet pipe or outlet pipe manifold.

If not, in order for aspiration and/or irrigation of the wound bed tooccur, it is appropriate for one or more bores, channels, conduits,passages, pipes, tubes, tubules and/or spaces, etc. to run from thepoint at which the fluid inlet pipe(s) and outlet pipe(s) pass throughand/or under the wound-facing face of the backing layer through oraround the wound filler under the backing layer.

Less usually, the wound filler may be an open-cell foam with pores thatmay form such bores, channels, conduits, passages and/or spaces throughthe wound filler under the backing layer.

Where the filler is or comprises one or more conformable hollow bodiesdefined by, for example a polymer film, sheet or membrane, it may beprovided with means for admitting fluids to the wound bed under thewound dressing.

These may be in the form of pipes, tubes, tubules or nozzles runningfrom the point at which the fluid inlet pipe(s) and outlet pipe(s) passthrough and/or under the wound-facing face of the backing layer throughor around the wound filler under the backing layer.

All of the suitable layouts for shallower wounds that compriseblind-bore, perforated inlet pipe or outlet pipe manifolds that aspiratefluid in the wound when the dressing is in use, that are describedhereinbefore, may be used under a wound filler under the backing layer.

In brief, suitable layouts include ones where one or both manifolds areannular or toroidal (regular, e.g. elliptical or circular or irregular),optionally with blind-bore, perforated radial tubes, pipes or nozzles,branching from the annulus or torus; and/or in a meandering, tortuous,winding, zigzag, serpentine or boustrophedic (i.e. in the manner of aploughed furrow) pattern, or defined by slots in and apertures throughlayers attached to each other in a stack.

The inlet and/or outlet tubes, the fluid tube and the fluid supply tube,etc. may be of conventional type, e.g. of elliptical or circularcross-section, and may suitably have a uniform cylindrical bore,channel, conduit or passage throughout their length, and suitably thelargest cross-dimension of the bore may be up to 10 mm for large torsowounds, and up to 2 mm for limb wounds.

The tube walls should suitably thick enough to withstand any positive ornegative pressure on them. However, the prime purpose of such tubes isto convey fluid irrigant and exudate through the length of the apparatusflow path, rather than to act as pressure vessels. The tube walls maysuitably be at least 25 micron thick.

The bore or any perforations, apertures, holes, openings, orifices,slits or slots along the pipes, etc. or in the hollow body or each ofthe hollow bodies may be of small cross-dimension. They may theneffectively form a macroscopic and/or microscopic filter forparticulates including cell debris and micro-organisms, whilst allowingproteins and nutrients to pass through.

Such tubes, pipes or hoses, etc. through and/or around the filler,whether the latter is a solid integer and/or one or more resilientlyflexible or conformable hollow bodies, are described in further detailhereinbefore in connection with the inlet pipe(s) and outlet pipe(s).

The whole length of the apparatus for aspirating, irrigating and/orcleansing wounds should be microbe-impermeable once the wound dressingis over the wound in use. It is desirable that the wound dressing andthe interior of the apparatus for aspirating, irrigating and/orcleansing wounds of the present invention is sterile.

The fluid may be sterilised in the fluid reservoir and/or the rest ofthe system in which the fluid moves by ultraviolet, gamma or electronbeam irradiation.

This way, in particular reduces or eliminates contact of internalsurfaces and the fluid with any sterilising agent.

Examples of other methods of sterilisation of the fluid also includee.g. the use of: ultrafiltration through microapertures or micropores,e.g. of 0.22 to 0.45 micron maximum cross-dimension, to be selectivelyimpermeable to microbes; and fluid antiseptics, such as solutions ofchemicals, such as chlorhexidine and povidone iodine; metal ion sources,such as silver salts, e.g. silver nitrate; and hydrogen peroxide;although the latter involve contact of internal surfaces and the fluidwith the sterilising agent.

It may be desirable that the interior of the wound dressing, the rest ofthe system in which the fluid moves, and/or the wound bed, even for awound in a highly exuding state, are kept sterile after the fluid issterilised in the fluid reservoir, or that at least naturally occurringmicrobial growth is inhibited.

Thus, materials that are potentially or actually beneficial in thisrespect may be added to the irrigant initially, and as desired theamount in increased by continuing addition. Examples of such materialsinclude antibacterial agents (some of which are listed above), andantifungal agents. Amongst those that are suitable are, for exampletriclosan, iodine, metronidazole, cetrimide, chlorhexidine acetate,sodium undecylenate, chlorhexidine and iodine.

Buffering agents, such as potassium dihydrogen phosphate/disodiumhydrogen phosphate. may be added to adjust the pH, as may localanalgesics/anaesthetics, such as lidocaine/lignocaine hydrochloride,xylocaine (adrenaline, lidocaine) and/or anti-inflammatories, to reducewound pain or inflammation or pain associated with the dressing.

In order to combat the deposition of materials in the flow path from theirrigant, a repellent coating may be used at any point or on any integerin the path in direct contact with the fluid, e.g. on the means forproviding aspiration and/or irrigation of the wound or any desired tubeor pipe.

Examples of coating materials for surfaces over which the aspiratingfluid passes include anticoagulants, such as heparin, and high surfacetension materials, such as PTFE, and polyamides, which are useful forgrowth factors, enzymes and other proteins and derivatives.

The apparatus of the invention for aspirating, irrigating and/orcleansing wounds is provided with means for admitting fluids directly orindirectly to the wound under the wound dressing in the form of a fluidsupply tube to a fluid reservoir.

The fluid reservoir for the irrigant may be of any conventional type,e.g. a tube, bag (such as a bag typically used for blood or bloodproducts, e.g. plasma, or for infusion feeds, e.g. of nutrients),chamber, pouch or other structure, e.g. of polymer film, which cancontain the irrigant fluid. The reservoir may be made of a film, sheetor membrane, often with a (generally uniform) thickness similar to thatof films or sheets used in conventional wound dressing backing layers,i.e. up to 100 micron, preferably up to 50 micron, more preferably up to25 micron, and of 10 micron minimum thickness, and is often aresiliently flexible, e.g. elastomeric, and preferably soft, hollowbody.

In all embodiments of the apparatus the type and material of the tubesthroughout the apparatus of the invention for aspirating, irrigatingand/or cleansing wounds and the fluid reservoir will be largelydetermined by their function.

To be suitable for use, in particular on chronic timescales, thematerial should be non-toxic and biocompatible, inert to any activecomponents, as appropriate of the irrigant from the fluid reservoirand/or wound exudate in the apparatus flow path, and, in any use of atwo-phase system aspiration and irrigation unit, of the dialysate thatmoves into the aspirating fluid in the apparatus.

When in contact with irrigant fluid, it should not allow any significantamounts of extractables to diffuse freely out of it in use of theapparatus.

It should be sterilisable by ultraviolet, gamma or electron beamirradiation and/or with fluid antiseptics, such as solutions ofchemicals, fluid- and microbe-impermeable once in use, and flexible.

Examples of suitable materials for the fluid reservoir include syntheticpolymeric materials, such as polyolefins, such as polyethylene, e.g.high density polyethylene and polypropylene.

Suitable materials for the present purpose also include copolymersthereof, for example with vinyl acetate and mixtures thereof. Suitablematerials for the present purpose further include medical gradepoly(vinyl chloride).

Notwithstanding such polymeric materials, the fluid reservoir will oftenhave a stiff area to resist any substantial play between it andcomponents that are not mutually integral, such as the fluid supply tubetowards the wound dressing, and may be stiffened, reinforced orotherwise strengthened, e.g. by a projecting boss.

Materials deleterious to wound healing that are removed includeoxidants, such as free radicals, e.g. peroxide and superoxide; iron IIand iron Ill; all involved in oxidative stress on the wound bed;proteases, such as serine proteases, e.g. elastase and thrombin;cysteine proteases; matrix metalloproteases, e.g. collagenase; andcarboxyl (acid) proteases; endotoxins, such as lipopolysaccharides;autoinducer signalling molecules, such as homoserine lactonederivatives, e.g. oxo-alkyl derivatives; inhibitors of angiogenesis suchas thrombospondin-1 (TSP-1), plasminogen activator inhibitor, orangiostatin (plasminogen fragment); pro-inflammatory cytokines such astumour necrosis factor alpha (TNFα) and interleukin 1 beta (IL-1β),oxidants, such as free radicals, e.g. peroxide and superoxide; and metalions, e.g. iron II and iron Ill, all involved in oxidative stress on thewound bed.

It is believed that aspirating wound fluid aids in removal from of thematerials deleterious to wound healing from wound exudate and/orirrigant, whilst distributing materials that are beneficial in promotingwound healing in contact with the wound.

A steady state concentration equilibrium of materials beneficial inpromoting wound healing may be set up between in the irrigant and/orwound exudate. Aspirating wound fluid aids in the quicker attainment ofthis equilibrium.

Materials beneficial to wound healing that are distributed includecytokines, enzymes, growth factors, cell matrix components, biologicalsignalling molecules and other physiologically active components of theexudate and/or materials in the irrigant that are potentially oractually beneficial in respect of wound healing, such as nutrients forwound cells to aid proliferation, gases, such as oxygen.

The conduits through which respectively the irrigant and/or woundexudate passes to and from the wound dressing and i) may have means formodular disconnection and withdrawal of the dressing, ii) providing animmediate fluid-tight seal or closure over the ends of the conduits andthe cooperating tubes in the rest of the apparatus of the invention soexposed, to prevent continuing passage of irrigant and/or exudate.

The outlet from the means for aspirate flow regulation and/or tubes maybe collected and monitored and used to diagnose the status of the woundand/or its exudate.

Any aspirate collection vessel may be of any conventional type, e.g. atube, bag (such as a bag typically used as an ostomy bag), chamber,pouch or other structure, e.g. of polymer film, which can contain theirrigant fluid that has been bled off. In all embodiments of theapparatus, the type and material of the aspirate collection vessel willbe largely determined by its function.

To be suitable for use, the material need only be fluid-impermeable oncein use, and flexible.

Examples of suitable materials for the fluid reservoir include syntheticpolymeric materials, such as polyolefins, such as poly (vinylidenechloride).

Suitable materials for the present purpose also include polyethylene,e.g. high-density polyethylene, polypropylene, copolymers thereof, forexample with vinyl acetate and mixtures thereof

In a further aspect of the present invention there is provided aconformable wound dressing, characterized in that it comprises: -abacking layer with a wound-facing face which is capable of forming arelatively fluid-tight seal or closure over a wound and has at least onepipe, which passes through and/or under the wound facing face to allowirrigation and/or aspiration of the wound; the point at which at leastone pipe passes through and/or under the wound-facing face forming arelatively fluid-tight seal or closure over the wound; and means forapplying high frequency vibrational, in particular ultrasonic, energy tothe wound bed when in use.

The dressing is advantageously provided for use in a bacteria-proofpouch.

Examples of suitable forms of such wound dressings are as described byway of example hereinbefore.

In a third aspect of the present invention there is provided a method oftreating wounds to promote wound healing using the apparatus foraspirating, irrigating and/or cleansing wounds of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described by way of example only withreference to the accompanying drawings in which, in all schematics, anysonode or sonode-transducer is omitted for clarity.

FIG. 1 a is a schematic view of an apparatus for aspirating, irrigatingand/or cleansing a wound according to the first aspect of the presentinvention that has a single device for moving fluid through the woundapplied to the aspirate in the fluid offtake tube downstream of and awayfrom the wound dressing, in combination with means for supply flowregulation, connected to a fluid supply tube, and means for aspirateflow regulation, connected to a fluid offtake tube. FIG. 1 b is asection view of the apparatus of FIG. 1 a.

FIG. 2 is a schematic view of another apparatus for aspirating,irrigating and/or cleansing a wound according to the first aspect of thepresent invention that has a first device for moving fluid through thewound applied to the aspirate in the fluid offtake tube downstream ofand away from the wound dressing, with means for aspirate flowregulation, connected to a fluid offtake tube; and a second device formoving fluid through the wound applied to the irrigant in the fluidsupply tube upstream of and towards the wound dressing.

FIGS. 3 to 7 are cross-sectional views of conformable wound dressings,of the second aspect of the present invention for aspirating and/orirrigating wounds. FIGS. 8 a to 8 c show another example embodiment of aconformable wound dressing, of the second aspect of the presentinvention for aspirating and/or irrigating wounds.

FIG. 9A to D are variants of a two-pump system with essentiallyidentical, and identically numbered, components as in FIG. 2, exceptthat there is a pump bypass loop, a filter downstream of the aspiratecollection vessel, and a bleed regulator, such as a rotary valve,connected to the fluid offtake tube or to the wound space, for theregulation of the positive or negative pressure applied to the wound.

FIG. 10A to C are variants of a two-pump system with essentiallyidentical, and identically numbered, components as in FIG. 11, exceptthat they have various means for varying the regulation of the positiveor negative pressure applied to the wound.

FIGS. 11A and B are variants of a two-pump system with essentiallyidentical, and identically numbered, components as in FIGS. 9A to 90.However, they have alternative means for handling the aspirate flow tothe aspirate collection vessel under negative or positive pressure tothe wound in simultaneous aspiration and irrigation of the wound,including in FIG. 11B a third device for moving fluid into a waste bag.

FIG. 12 is a single-pump system essentially with the omission from theapparatus of FIG. 11 of the second device for moving irrigant fluid intothe wound dressing.

FIG. 13 shows a suitable apparatus for in vitro assessment of theeffects of ultrasound on cells in a simulated wound.

FIG. 14 shows an example format for a transducer including a focusingelement for focusing the propagation of ultrasound at a predeterminedangle.

DETAILED DESCRIPTION

Referring to FIGS. 1 a and 1 b, the apparatus (1) for aspirating,irrigating and/or cleansing wounds comprises a conformable wounddressing (2), having a backing layer (3) which is capable of forming arelatively fluid-tight seal or closure (4) over a wound (5) and oneinlet pipe (6) for connection to a fluid supply tube (7), which passesthrough the wound-facing face of the backing layer (5) at (8), and oneoutlet pipe (9) for connection to a fluid offtake tube (10), whichpasses through the wound-facing face at (11), the points (8), (11) atwhich the inlet pipe and the outlet pipe passes through and/or under thewound-facing face forming a relatively fluid-tight seal or closure overthe wound; the inlet pipe being connected via means for supply flowregulation, here a valve (14), by the fluid supply tube (7) to a fluidreservoir (12), and the outlet pipe (9) being connected via means foraspirate flow regulation, here a valve (16) and a fluid offtake tube(10) to waste, e.g. to a waste reservoir (19), such as a collection bag;a device for moving fluid through the wound (17), here a diaphragm pump(18), e.g. preferably a small portable diaphragm pump, acting on thefluid aspiration tube (13) to apply a low negative pressure on thewound; and the valve (14) in the fluid supply tube (7), the valve (16)in the fluid offtake tube (10), and the diaphragm pump (18), providingmeans for providing simultaneous aspiration and irrigation of the wound(17), such that fluid may be supplied to fill the flow path from thefluid reservoir via the fluid supply tube (via the means for supply flowregulation) and moved by the device through the flow path.

The operation of the apparatus is as described herein before.

Referring to FIG. 2, the apparatus (21) is a variant two-pump systemwith essentially identical, and identically numbered, components as inFIG. 1, except that there is no means for supply flow regulation in thefluid supply tube (7) from the fluid reservoir (128), and there is afirst device for moving fluid through the wound (17), here a diaphragmpump (18A), e.g. preferably a small portable diaphragm pump, acting onthe fluid aspiration tube (13) downstream of and away from the wounddressing to apply a low negative pressure on the wound; with means foraspirate flow regulation here a valve (16) connected to the fluidofftake tube (10) and a vacuum vessel (aspirate collection jar) (12A);and a second device for moving fluid through the wound (17), here aperistaltic pump (188), e.g. preferably a small portable diaphragm pump,applied to the irrigant in the fluid supply tube (7) upstream of andtowards the wound dressing, the first device (18A) and second device(188), and the valve (16) in the fluid offtake tube (10), and thediaphragm pump (18), providing means for providing simultaneousaspiration and irrigation of the wound (17), such that fluid may besupplied to fill the flow path from the fluid reservoir via the fluidsupply tube (via the means for supply flow regulation) and moved by thedevices through the flow path.

The operation of the apparatus is as described hereinbefore

Referring to FIG. 3, a form of dressings for deeper wounds is shown.This comprises a circular backing layer (342) and a chamber (363) in theform of a deeply indented disc much like a multiple Maltese cross.

This is defined by an upper impervious membrane (361) and a lower porousfilm (362) with apertures (364) that deliver the irrigant fluid directlyfrom the wound bed over an extended area.

The chamber (363) is able to conform well to the wound bed by the armsclosing in and possibly overlapping in insertion into the wound. Thespace above the chamber (363) is filled with an elastically resilientfoam or loose gauze.

A piezoelectric sonode-transducer (111) is mounted on the upper face ofthe backing layer (342), and is connected to an ultrasonic frequencyelectrical signal generator run at the appropriate frequencies (112)(shown schematically) by electrical leads (113).

It is a sheet or membrane of a piezoelectric transducing polyolefin,such as polyvinylidene fluoride and copolymers thereof, and is adheredwith a curable adhesive to the dressing.

An inlet pipe (346) and outlet pipe (347) are mounted centrally in aboss (351) on the sonode-transducer (111) on the backing layer (342),and pass through both.

The inlet pipe (346) communicates with the interior of the chamber(348). The outlet pipe (347) extends radially to just below the backinglayer (342) to communicate with the interior of the pouch (363).

Referring to FIG. 4, this form of the dressing is provided with a woundfiller (348) under a circular backing layer (342).

The filler (348) comprises a generally downwardly domed toroidalconformable hollow body, defined by a membrane (349) which is filledwith a fluid, here air or nitrogen that urges it to the wound shape. Thefiller (348) is permanently attached to the backing layer via a boss(351), which is e.g. heat-sealed to the backing layer (342).

An annular layer of foam (364) formed of a suitable material, e.g. aresilient thermoplastic, surrounds the boss (351). Preferred foammaterials include reticulated filtration polyurethane foams with smallapertures or pores.

A piezoelectric sonode-transducer (111) is mounted on the underside ofthe boss (351), and is connected to an ultrasonic frequency electricalsignal generator run at the appropriate frequencies (112) (shownschematically) by electrical leads (113) running through the boss (351).

It is a sheet or membrane of a piezoelectric transducing polyolefin,such as polyvinylidene fluoride and copolymers thereof, and is adheredby heat lamination to the dressing.

An inflation inlet pipe (350), inlet pipe (346) and outlet pipe (347)are mounted centrally in the boss (351) in the backing layer (342). Theinflation inlet pipe (350) communicates with the interior of the hollowbody (348), to permit inflation of the body (348). The inlet pipe (346)extends in a pipe (352) through boss (351).

The outlet pipe (347) extends radially immediately under the backinglayer (342), and collects fluid flowing radially through the foam layer(364) from the wound periphery when the dressing is in use.

Referring to FIG. 5, this form of the dressing is a variant of that ofFIG. 4, with identical, and identically numbered, components, except forthe following:

A downwardly domed membrane (361) with apertures (362) is permanentlyattached at its periphery by heat-sealing to, and lies underneath, thefiller (348), to form an inlet manifold (353). The pipe (352)communicates with the interior of the inlet manifold (353), but notthrough the piezoelectric sonode-transducer (111).

This is still mounted on the underside of the boss (351), but spacedfrom it by struts (372) defining peripheral channels or conduits (363)that communicate between the pipe (352) and the inlet manifold (353).Referring to FIG. 6, the dressing is also provided with a wound filler(348) under a circular backing layer (342). This comprises a generallyoblately spheroidal conformable hollow body, defined by a membrane (349)which is filled with a fluid, here air or nitrogen, that urges it to thewound shape. The filler (348) is permanently attached to the backinglayer via a boss (351), which is e.g. heat-sealed to the backing layer(342).

An inflation inlet pipe (350), inlet pipe (346) and outlet pipe (347)are mounted centrally in the boss (351) in the backing layer (342) abovethe hollow body (348). The inflation inlet pipe (350) communicates withthe interior bf the hollow body (348), to permit inflation of the body(348). The inlet pipe (346) extends in a pipe (352) effectively throughthe hollow body (348). The outlet pipe (347) extends radiallyimmediately under the backing layer (342).

The lower end of the inlet pipe (346) is splayed into a funnel (356), inpart of the wall of which is a recess (357). A sonode-transducer, suchas an Exogen™ device (111) is a tight push fit in the recess.

It is connected to an ultrasonic frequency electrical signal generatorrun at the appropriate frequencies (112) (shown schematically) byelectrical leads (113) running through the boss (351) and the hollowbody (348).

Referring to FIG. 7, this form of the dressing is a variant of that ofFIG. 6, with identical, and identically numbered, components, exceptthat the sonode-transducer, whilst mounted in the same overall positionis not in a recess, but within the hollow body (348).

This form of the dressing is a more suitable layout for deeper wounds.

Referring to FIG. 8 a, another form for deeper wounds is shown.

This comprises a circular, or more usually square or rectangular backinglayer (342) and a chamber (363) in the form of a deeply indented discmuch like a multiple Maltese cross or a stylized rose.

This is defined by an upper impervious membrane (361) and a lower porousfilm (362) with apertures (364) that deliver the irrigant fluid directlyto the wound bed over an extended area, and thus effectively forms aninlet manifold. Three configurations of the chamber (363) are shown inFIG. 8 b, all of which are able to conform well to the wound bed by thearms closing in and possibly overlapping in insertion into the wound.

The space above the chamber (363) is filled with a wound filler (348)under the backing layer (342). This comprises an oblately spheroidalconformable hollow body, defined by a membrane (349) that is filled witha fluid, here air or nitrogen, that urges it to the wound shape.

A piezoelectric sonode-transducer (111) is mounted on the upper face ofthe backing layer (342), and is connected to an ultrasonic frequencyelectrical signal generator run at the appropriate frequencies (112)(shown schematically) by electrical leads (113).

It is a sheet or membrane of a piezoelectric transducing polyolefin,such as polyvinylidene fluoride and copolymers thereof, and is adheredwith a curable adhesive to the dressing.

A moulded hat-shaped boss (351) is mounted centrally on the upperimpervious membrane (361) of the chamber (363). It has three internalchannels, conduits or passages through it (not shown), each with entryand exit apertures. The filler (348) is attached to the membrane (361)of the chamber (363) by adhesive, heat welding or a mechanical fixator,such as a cooperating pin and socket.

An inflation inlet pipe (350), inlet pipe (346) and outlet pipe (347)pass under the edge of the proximal face of the backing layer (342) ofthe dressing, and extend radially immediately under the filler (348) andover the membrane (361) of the chamber (363) to each mate with an entryaperture in the boss (351).

An exit to the internal channel, conduit or passage through it thatreceives the inflation inlet pipe (350) communicates with the interiorof the hollow filler (348), to permit inflation.

An exit to the internal channel, conduit or passage that receives theinlet pipe (346) communicates with the interior of the chamber (363) todeliver the irrigant fluid via the chamber (363) to the wound bed overan extended area.

Similarly, an exit to the internal channel, conduit or passage thatreceives the outlet pipe (347) communicates with the space above thechamber (363) and under the wound filler (348), and collects flow ofirrigant and/or wound exudate radially from the wound periphery.

Referring to FIG. 9A, the apparatus (21) is a variant two-pump systemwith essentially identical, and identically numbered, components as inFIG. 2.

Thus, there is a means for supply flow regulation, here a valve (14) inthe fluid supply tube (7) from the fluid reservoir (128), and a firstdevice for moving fluid through the wound (17), here a fixed-speeddiaphragm pump (18A), e.g. preferably a small portable diaphragm pump,acting not on the fluid aspiration tube (13), but on an air aspirationtube (113) downstream of and away from an aspirate collection vessel(12A) to apply a low negative pressure on the wound through the aspiratecollection vessel (12A); with a second device for moving fluid throughthe wound (17), here a fixed speed peristaltic pump (188), e.g.preferably a small portable peristaltic pump, applied to the irrigant inthe fluid supply tube (7) upstream of and towards the wound dressing,the first device (18A) and second device (188), and the valve (14) inthe fluid supply tube (7), providing means for providing simultaneousaspiration and irrigation of the wound (17), such that fluid may besupplied to fill the flow path from the fluid reservoir via the fluidsupply tube (via the means for supply flow regulation) and moved by thedevices through the flow path.

There is no means for aspirate flow regulation; e.g. a valve connectedto the fluid offtake tube (10).

Since first device (18A) and second device (188) are fixed-speed, thevalve (14) in the fluid supply tube (7) provides the sole means forvarying the irrigant flow rate and the low negative pressure on thewound.

The following extra features are present:

The second device, the fixed-speed peristaltic pump (18B), is providedwith means for avoiding over-pressure, in the form of a bypass loop witha nonreturn valve (115). The loop runs from the fluid supply tube (7)downstream of the pump (18B) to a point in the fluid supply tube (7)upstream of the pump (18B).

A pressure monitor (116) connected to the fluid offtake tube (10) has afeedback connection to a bleed regulator, here a motorised rotary valve(117) on a bleed tube (118) running to and centrally penetrating the topof the aspirate collection vessel (12A). This provides means for holdingthe low negative pressure on the wound at a steady level.

A filter (119) downstream of the aspirate collection vessel (12A)prevents passage of gas-(often air-) borne particulates, includingliquids and micro-organisms, from the irrigant and/or exudate thatpasses into the aspirate collection vessel (12A) into the first device(18A). At the same time, it allows the carrier gas to pass through theair aspiration tube (113) downstream of it to the first device (18A).

The operation of the apparatus is as described hereinbefore

Referring to FIG. 98, this shows an alternative layout of theessentially identical, and identically numbered, components in FIG. 9Adownstream of point A in FIG. 9A. The bleed tube (118) runs to the airaspiration tube (113) downstream of the filter (119), rather than intothe aspirate collection vessel (12A). This provides means for holdingthe low negative pressure on the wound at a steady level. The operationof the apparatus is as described hereinbefore.

Referring to FIG. 9C, this shows an alternative layout of theessentially identical, and identically numbered, components in FIG. 9Aupstream of point B in FIG. 9A. The second device (188) is avariable-speed pump, and the valve (14) in the fluid supply tube (7) isomitted. The second device (188) is the sole means for varying theirrigant flow rate and the low negative pressure on the wound. Theoperation of the apparatus is as described hereinbefore

Referring to FIG. 90, this shows an alternative layout of theessentially identical, and identically numbered, components in FIG. 9Adownstream of point 8 in FIG. 9A.

The pressure monitor (116) is connected to a monitor offtake tube (120)and has a feedback connection to the bleed regulator, motorised rotaryvalve (117) on a bleed tube (118) running to the monitor offtake tube(120). This provides means for holding the low negative pressure on thewound at a steady level. The operation of the apparatus is as describedhereinbefore.

Referring to FIG. 10A, this shows another alternative layout of theessentially identical, and identically numbered, components in FIG. 9Adownstream of point 8 in FIG. 9A.

The pressure monitor (116) is connected to a monitor offtake tube (120)and has a feedback connection to a means for aspirate flow regulation,here a motorised valve (16) in the air aspiration tube (113) downstreamof the filter (119).

This provides means for aspirate flow regulation and for holding the lownegative pressure on the wound at a steady level. The operation of theapparatus is as described hereinbefore

Referring to FIG. 10B, this shows another alternative layout of theessentially identical, and identically numbered, components in FIG. 10Adownstream of point B in FIG. 9A. The pressure monitor (116) isconnected to a monitor offtake tube (120) and has a feedback connectionto a means for aspirate flow regulation, here a motorised valve (16), inthe fluid offtake tube (10) upstream of the aspirate collection vessel(12A).

This provides means for aspirate flow regulation and for holding the lownegative pressure on the wound at a steady level. The operation of theapparatus is as described hereinbefore

Referring to FIG. 10C, this shows another alternative layout of theessentially identical, and identically numbered, components in FIG. 10Adownstream of point B in FIG. 9A. The pressure monitor (116) isconnected to a monitor offtake tube (120) and has a feedback connectionto a variable-speed first device (1 SA), here a variable-speed pump,downstream of the filter (119), and the valve (16) in the fluid offtaketube (10) is omitted.

This provides means for aspirate flow regulation and for holding the lownegative pressure on the wound at a steady level. The operation of theapparatus is as described hereinbefore.

Referring to FIG. 11A, this shows another alternative layout of theessentially identical, and identically numbered, components in FIG. 10Cdownstream of point B in FIG. 9A, and alternative means for handling theaspirate flow to the aspirate collection vessel under negative orpositive pressure to the wound. The pressure monitor (116) is connectedto a monitor offtake tube (120) and has a feedback connection to avariable speed first device (18A), here a variable-speed pump, upstreamof the aspirate collection vessel (12A), and the filter (119) and theair aspiration tube (113) are omitted. This provides means for aspirateflow regulation and for holding the low negative pressure on the woundat a steady level. The operation of the apparatus is as describedhereinbefore.

Referring to FIG. 11B, this shows another alternative layout of theessentially identical, and identically numbered, components in FIG. 10Cdownstream of point B in FIG. 9A, and alternative means for handling theaspirate flow to the aspirate collection vessel under negative orpositive pressure to the wound. The pressure monitor (116) is omitted,as is the feedback connection to a variable-speed first device (18A),here a variable speed pump, downstream of the aspirate collection vessel(12A) and the filter (119).

A third device (18C), here a fixed-speed pump, provides means for movingfluid from the aspirate collection vessel (12A) into a waste bag (12C).The operation of the apparatus is as described herein before.

Referring to FIG. 12, this shows an alternative layout of theessentially identical, and identically numbered, components in FIG. 9Aupstream of point A in FIG. 9A.

It is a single-pump system essentially with the omission from theapparatus of FIG. 9A of the second device for moving irrigant fluid intothe wound dressing. The operation of the apparatus is as describedhereinbefore.

Referring to FIG. 13, a suitable apparatus for assessing the effects ofultrasound treatment on cells in a simulated wound is shown.

Pump (188) pumps irrigation fluid from an irrigant reservoir (12)through a 3-way valve (14), which can be configured to allow continuousflow through the test chamber (400), emptying of the test chamber (400)under vacuum, or emptying of the test chamber (400) at atmosphericpressure.

The irrigant passes into the test chamber (400), which is described inmore detail later. The aspirate leaving the test chamber (400) passesinto a waste reservoir (19). A source of vacuum (18A) is used tomaintain the system at a vacuum (950 mbar), and draws the aspirate fromthe test chamber (400) into the waste reservoir (19). This source ofvacuum (18A) is typically a vacuum pump. An additional pump (401)recycles the aspirate from the waste reservoir (19) to the irrigantreservoir (12). This system is useful in a test apparatus, but wouldgenerally not be suitable when treating a patient as the aspirate wouldtypically be contaminated and should be disposed of

An apparatus of the present invention was constructed essentially as inFIG. 13. The circuit shown in FIG. 13 can be used for either sequentialor simultaneous irrigation/aspiration.

The circuit has the means for fluid cleansing of a wound using anapparatus where an irrigant or fluid of some nature is deliveredcontinually to the (simulated) wound bed and the resultant woundexudate/fluid mixture is at the same time continually aspirated from thewound and is pumped to waste. (For the experiments the aspirant was notpumped to waste but was re-circulated.) The circuit was also used toprovide a system where the wound is subjected to repeated iteration of acycle of fluid delivery followed by a period of aspiration under reducedpressure.

The apparatus comprises a surrogate wound chamber (400) (Minucellsperfusion chamber) in which normal diploid human fibroblasts werecultured on 13 mm diameter (Thermanox polymer) cover slips retained in atwo part support (Minucell Minusheets). Tissues present in the healingwound that must survive and proliferate were represented by the cellswithin the chamber. Nutrient medium (DMEM with 5% FCS with 1% BufferAll) to simulate an irrigant fluid/wound exudate mixture was pumped froma reservoir into the lower aspect of the chamber where it bathed thefibroblasts and was removed from the upper aspect of the chamber andreturned to a second reservoir. The wound chamber was maintained at lessthan atmospheric pressure by means of a Vacuum pump in line with thecircuit.

The pumps for the circuit were peristaltic pumps acting on silicone (orequivalent) elastic tubing. The circuit was exposed to a vacuum of nomore than 10% atmospheric pressure (950 mbar and atmospheric pressurevaried up to a maximum value of 1044 mbar.) The internal diameter of thetubing was 1.0 mm. A total volume for the circuit including the chamberand the reservoir was between 50 and 220 ml. The flow rates used were at0.2 ml

The circuit also comprised upstream of the wound chamber, a heatexchanger such that the temperature of the nutrient media bathing thecells reaches between 35° C. and 37° C.

Experiments were conducted that simulated conditions not uncommon forhealing wounds whereby the chamber simulating the wound was subjected >to stimulation QY ultrasound waves representing the Exogen Ultrasound(Smith & Nephew) device signal for a period of time not greater than 20min. These experiments were performed using both sequential (SEQ) andsimultaneous (SIA) irrigation/aspiration.

Method in More Detail

Using simultaneous irrigate/aspirate (SIA) and sequentialirrigate/aspirate (SEQ) systems the effect of ultrasound treatment onfibroblast proliferation was determined.

Cells

Human dermal fibroblasts (HS8/BS04) grown at 37° C./5% CO₂, in T175flasks containing 35 ml DMEM/10% FCS media were washed in PBS and liftedusing 1× trypsin/EDTA (37° C. for 5 min). Trypsin inhibition wasachieved by adding 10 ml DMEM/10% FCS media and the cells pelleted bycentrifugation (Hereus Megafuge 1.0 R; 1000 rpm for 5 min). The mediawas discarded and cells re-suspended in 10 ml DMEM/10% FCS. Cells werecounted using haemocytometer and diluted in DMEM/10% FCS to obtain100,000 cells per ml.

Cells (100 μl of diluted stock) were transferred to 13 mm Thermanoxtissue culture coated cover slips (cat. 174950, lot 591430) in a 24 wellplate and incubated at 37° C. in 5% CO² to allow for cell adherence.After 1 h, 1 ml DMEM/10% FCS media was added per well and the cellsincubated for approximately 5 hours in the above conditions. Cells wereserum starved overnight by removing the DMEM/10% FCS and washing thecoverslips with 2×1 ml PBS prior to the addition of 1 ml DMEM/O % FCS.

Following overnight incubation, cells were assessed visually for celladherence under the microscope and those with good adherence wereinserted into cover slip holders for assembly in the Minucell chamber. Anumber of coverslips (n=6) were removed to determine the baseline WSTactivity.

Media

Cells were grown in DMEM media (Sigma, no. 06429) supplemented with 5%foetal calf serum; 1-glutamine, non-essential amino acids andpenicillin/streptomycin (various lot numbers). Media used in theexperimental systems was buffered with Buffer-All media (Sigma, lot51k2311) to ensure stable pH of the media.

Minucell Flow Systems

Media (50 ml) was transferred to each bottle prior to the autoclavedsystems being assembled. The Minucell chambers were filled with 4 mlmedia prior to coverslips being inserted. The systems were set-up asshown in FIG. 1 (pump 1, asset 5715; pump 2, asset 4586 set to run at0.2 ml/min; hot plates asset were set to 45° C.; Discofix 3-way valves(Arnolds lot 04A2092042 c/z); vacuum pump, llmvac VCZ 310 (set to 950mbar).

SEQ Systems (i.e. Sequential Irrigation/Aspiration)

Media was pumped through the systems at 0.2 ml/min continuously when thechambers were full. The Minucell chambers were emptied by disconnectingthe tubing from the pump and switching the 3-way valve to allow airthrough an attached 0.22 μm filter. When fully emptied, the 3-way valvewas switched to close the system between the valve and the pump and soallowing the formation of a vacuum in the system. Elevation of the 663-way valve ensured media did not pass through the 0.22 μm filter bygravity flow. After 1 h, the 3-way valve was switched back to thestarting position to allow the Minucell chamber to fill and the tubereconnected to the pump. The SEQ systems were treated as per Table 1.

TABLE 1 FILL/EMPTY REGIME FOR SEQ SYSTEM MINUCELL CHAMBERS Time (h) 0 12 3 4 5 6 7 8 20 21 22 23 24 Emp- F E F E F E F E F E F E W A ty/ fillF, full chamber, flowing; E, empty chamber, under vacuum; W, removecoverslips for WST assay; A, read WST assay result.SIA Systems (i.e. Simultaneous Irrigate/Aspirate)

Continuous irrigate aspirate systems were run for 24 h with mediairrigating the cells and being aspirated under vacuum set to 950 mbar.The atmospheric pressure varied daily, up to a maximum value of 1048mbar, therefore the difference in pressure between the systems and theatmosphere was always under 10%.

Ultrasound Treatment

Whilst media was circulating through the Minucell systems in the firsthour, Minucell chambers were placed onto the ultrasound device usingtransducers. The Minucell chambers received 20 minutes ultrasoundtreatment and were then placed on the hot-plates. The optimal intensityand wavelength for delivery to each Minucell chamber was determined tobe 1.5 MHz at a power (intensity) of 100 MW/CM². The ultrasoundproperties would generally have to be optimised for any particularapplication or wound dressing to take account of the properties of thewound and the dressing involved. The values used in the presentinvention were at a relatively high intensity to compensate for therelatively high attenuation in the experimental apparatus.

WST Assay

WST assay to measure the cells mitochondrial activity was performed onthe coverslips. WST reagent (Roche, lot 11264000) was diluted to 10% v/vin DMEM/10% FCS/buffer all media. The coverslips (n=6) were removed fromeach Minucell chamber and washed in 1 ml PBS. PBS was removed and 200 μlWST/DMEM media added. The coverslips were then incubated at 37° C. for45 min before transferring 150 μl to a 96 well plate. The absorbance at450 nm with reference at 655 nm was determined using Ascent MultiskanMicrotitre plate reader.

Results and Discussion

The mitochondrial activity of cells grown in SIA and SEQ systems, withor without ultrasound treatment was determined using the WST assay.

The WST activity of individual experiments is shown in Table 2. In boththe SIA and SEQ systems, the 20 min of ultrasound treatment stimulatedfibroblast proliferation, as determined by WST assay. Fibroblastproliferation was greater in the SIA system compared to SEQ system,which reflects data obtained previously. The summarized data in Table 2shows the stimulatory effect of ultrasound treatment was observed anumber of times i.e. in 3 repetitions.

TABLE 2 Mean of cell activity* Conditions after 25 hours. N = 3Continuous flow (SIA) flow 0.19 Continuous flow (SIA) plus) 0.23ultrasound Fill empty 6 cycles 0.05 Fill empty 6 cycles plus 0.11ultrasound *Cell activity measured with a WST (Tetrazolium basedmitochondrial dehdrogenase activity assay).

Treatment of fibroblasts with 20 min ultrasound signal increased rate ofproliferation after 24 hours.

The effect was observed in both SIA and SEQ flow systems.

Fibroblast activity in ultrasound stimulated SEQ system was still lessthan fibroblast activity in the un-stimulated SIA system.

Although the ultrasound signal stimulated fibroblast proliferation inthe SEQ system above that of the un-stimulated control system, the levelof fibroblast activity was still lower than the fibroblast activitydetermined in the un-stimulated SIA.

This experiment demonstrates the beneficial effects of applyingultrasound to a wound bed as it encourages the activity andproliferation of cell, thus promoting healing.

1.-45. (canceled)
 46. A wound dressing comprising: a wound coverconfigured to be placed over a wound; a manifold configured to bedisposed between the wound cover and the wound, the manifold configuredto conform to the shape of the wound, the manifold comprising aplurality of flow channels configured to aspirate fluid from the wound;an outlet tube configured to fluidically couple the manifold to anegative pressure source; and an ultrasonic transducer configured to bedisposed in the wound under the wound cover, the ultrasonic transducerconfigured to apply a vibrational energy to the wound.
 47. The dressingof claim 46, further comprising an inlet tube configured to fluidicallycouple the manifold to a fluid source, wherein the manifold furthercomprises a plurality of apertures configured to deliver fluid to thewound.
 48. The dressing of claim 47, further comprising a wound contactlayer configured to be positioned in direct contact with the wound andfurther configured to conform to the shape of the wound, the woundcontact layer comprising a plurality of apertures configured to allowfluid to pass through the wound contact layer.
 49. The dressing of claim46, wherein the ultrasonic transducer is configured to apply thevibrational energy while fluid is being aspirated from the wound throughthe manifold.
 50. The dressing of claim 46, wherein the ultrasonictransducer is configured to be positioned between the wound cover andthe manifold.
 51. The dressing of claim 46, wherein the ultrasonictransducer is configured to apply the vibrational energy at a frequencyof 5 Hz to 10 kHz.
 52. The dressing of claim 46, wherein the ultrasonictransducer is configured to apply the vibrational energy to the woundfor a period of about 20 minutes.
 53. The dressing of claim 46 furthercomprising the negative pressure source.
 54. A negative pressure woundtherapy device comprising: a conformable wound dressing configured toform a sufficiently fluid-tight seal over a wound; an outlet tubeconfigured to fluidically connect the wound to a negative pressuresource; a wound contact layer configured to be positioned in directcontact with the wound and further configured to conform to a shape ofthe wound, the wound contact layer comprising a plurality of aperturesconfigured to aspirate fluid from the wound when negative pressure isdelivered to the wound; and a vibrational energy generator configured toapply a vibrational energy to the wound contact layer, wherein afrequency and an intensity of the vibrational energy field are selectedfor the stimulation of the healing of the wound.
 55. The device of claim54, wherein the vibrational energy generator is configured to apply thevibrational energy while fluid is being aspirated from the wound throughthe wound contact layer.
 56. The device of claim 54, wherein theintensity selected for the stimulation of the healing of the wound isultrasound energy at spatial peak temporal average acoustic intensity of5-100 mW/cm².
 57. The device of claim 54, wherein the frequency selectedfor the stimulation of the healing of the wound is ultrasound energy ata frequency of 20 kHz to 10 MHz.
 58. The device of claim 54, wherein thevibrational energy generator is configured to pulse the vibrationalenergy at a frequency of 5 Hz to 10 kHz.
 59. The device of claim 54further comprising the negative pressure source.
 60. A method fortreating a wound comprising: positioning a wound dressing, the wounddressing comprising: a wound cover configured to form a sufficientlyfluid-tight seal over the wound; a manifold configured to be disposed inthe wound under the wound cover, the manifold comprising a plurality offlow channels configured to aspirate fluid from the wound; an outlettube configured to fluidically couple the manifold to a negativepressure source; and an ultrasonic transducer configured to be disposedbetween the manifold and the wound cover; operating the negativepressure source to cause application of negative pressure to the woundthrough the outlet tube; and operating the ultrasonic transducer tocause application of an ultrasonic energy to the wound.
 61. The methodof claim 60, wherein: the wound dressing further comprises an inlet tubeconfigured to fluidically couple the wound to a fluid source and themanifold further comprises a plurality of apertures configured todeliver fluid to the wound; and the method further comprising causingthe fluid to be delivered from the fluid source to the wound via themanifold.
 62. The method of claim 61 further comprising waiting for aperiod of time after causing delivery of fluid to the wound beforecausing application of negative pressure to the wound.
 63. The method ofclaim 62 further comprising delaying causing the delivery of theultrasonic energy to the wound until after fluid has been delivered tothe wound.
 64. The method of claim 63 further comprising causingapplication of negative pressure to the wound when the ultrasonic energyis being applied to the wound.
 65. The method of claim 60, wherein thevibrational energy is applied at a frequency of 5 Hz to 10 kHz.
 66. Themethod of claim 60, wherein the vibrational energy is applied to thewound for a period of about 20 minutes.